README: Re-introduce a NEMU specific README

This README markdown file is based on the topic/compile-reduced initial
NEMU README.

Based on the evolution of the project since the early NEMU days, this
new README version comes with:

- A small description of the virt i386 machine type.
- An updated list of guest platforms
- An updated list of guest OSes
- A shortened list of boot methods and firmware type support
- A slightly updated device model description

Fixes #69

Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

README.md

@@ -0,0 +1,213 @@
+- [NEMU, a cloud hypervisor](#nemu--a-cloud-hypervisor)
+  * [Rationale](#rationale)
+  * [QEMU base](#qemu-base)
+  * [*NEMU*](#-nemu-)
+  * [Requirements](#requirements)
+    + [High Level](#high-level)
+    + [Architectures](#architectures)
+    + [Guest OS](#guest-os)
+    + [Guest Platforms](#guest-platforms)
+    + [Host Platforms](#host-platforms)
+    + [Firmware and boot](#firmware-and-boot)
+    + [Boot methods](#boot-methods)
+    + [Memory](#memory)
+    + [Devices](#devices)
+      - [Models](#models)
+      - [Block](#block)
+    + [Guest Image Formats](#guest-image-formats)
+    + [Migration](#migration)
+    + [Monitoring](#monitoring)
+    + [**To be discussed**](#--to-be-discussed--)
+
+
+# NEMU, a cloud hypervisor
+
+*NEMU* is an open source hypervisor specifically built and designed to run modern cloud
+workloads on modern 64-bit Intel and ARM CPUs.
+
+## Rationale
+
+Modern guest operating systems that host cloud workloads run on virtual hardware platforms
+that do not require any legacy hardware. Additonally modern CPUs used in data centers have
+advanced virtualization features that have eliminated the need for most CPU emulation.
+
+There currently is no open source hypervisor solutions with a clear and narrow focus on
+running cloud specific workloads on modern CPUs. All available solutions have evolved over
+time and try to be fairly generic. They attempt to support a wide range of virtual hardware
+architectures and run on hardware that has varying degree of hardware virtualization support.
+This results in a need to provide a large set of legacy platforms and device models requiring
+CPU, device and platform emulation. As a consequence they are built on top of large and
+complex code bases.
+
+*NEMU* on the other hand aims to leverage KVM, be narrow focused on exclusively running modern,
+cloud native workloads, on top of a limited set of hardware architectures and platforms.
+It assumes fairly recent CPUs and KVM allowing for the the elimination of most emulation logic.
+
+This will allow for smaller code base, lower complexity and a reduced attack surface compared
+to existing solutions. It also gives more space for providing cloud specific optimizations and
+building a more performant hypervisor for the cloud. Reducing the size and complexity of the code
+allows for easier review, fuzz testing, modularization and future innovation.
+
+## QEMU base
+
+QEMU is the current de facto standard open source cloud hypervisor. It has a rich set of features
+that have been developed and tested over time. This includes features such as live migration,
+PCI, Memory, NVDIMM and CPU hotplug, VFIO, mediated device passthrough and vhost-user. QEMU also
+has been the code base on which significant effort and innovation has been invested to create multiple
+performant I/O models
+
+It also comes with a very large support for legacy features, for platforms and devices and is capable
+of running on a large number of hardware platforms. It also allows for cross platform emulation.
+One of its fundamental goal is about being as generic as possible and run on a large set of hardware
+and host a diversity of workloads. QEMU needed emulation support to be build into the code as hardware
+lacked critical virtualization features.
+
+QEMU allows for build time configuration of some of its rich feature set. However there is quite a
+large amount of the code base that cannot be compiled out as the emulated platforms make assumptions
+about certain legacy devices being always present. QEMU also has abstractions within the code to support
+all of these legacy features.
+
+## *NEMU*
+
+*NEMU* is based off QEMU and leverage its rich feature set, but with a much narrower focus.
+It leverages the performant, robust and stable QEMU codebase without the need to supporting the
+myriad of features, platforms and harware that are not relevant for the cloud.
+
+The goal of *NEMU* is to retain the absolute minimal subset of the QEMU codebase that is required
+for the feature set described below. The QEMU code base will also be simplified to reduce the number
+of generic abstractions.
+
+## Requirements
+
+*NEMU* provides a PCI virtio platform with support for vfio based device direct assigment and mediated
+device assigment support. It also aims to retain support for live migration, vhost-user and a build time
+configurable device hotplug support for PCI, memory, NVDIMM and CPU. *NEMU* will need to emulate a small
+subset of features including PCI host brige.
+
+*NEMU* also introduces a new QEMU x86-64 machine type: **`virt`**. It is a purely virtual platform, that
+does not try to emulate any existing x86 chipset or legacy bus (ISA, SMBUS, etc) and offloads as many features
+to KVM as possible. This is a similar approach as the already existin AArch64 `virt` machine type and *NEMU*
+will only support the two `virt` machine types.
+
+Below is a list of QEMU features that *NEMU* will retain and add.
+
+### High Level
+
+* KVM and KVM only based
+* Minimal emulation
+* Low latency
+* Low memory footprint
+* Low complexity
+* Small attack surface
+* 64-bit support only
+* Optional and build time configurable CPU, memory, PCI and NVDIMM hotplug
+* Machine to machine migration
+
+### Architectures
+
+*NEMU* only supports two 64-bit CPU architectures:
+* `x86-64`
+* `AArch64`
+
+### Guest OS
+* `64-bit Linux`
+
+### Guest Platforms
+
+* `virt` (x86-64) QEMU x86-64 virtual machine
+* `virt` (AArch64) QEMU AArch64 virtual machine
+
+### Host Platforms
+
+* `Linux`
+
+### Firmware and boot
+
+* `UEFI`
+* `ACPI`
+  * Hardware Reduced ACPI
+  * Optional hotplug support
+	* CPU
+	* Memory
+	* NVDIMM
+	* PCI devices
+	* VFIO
+	* vhost-user
+
+### Boot methods
+
+* `UEFI boot`
+
+### Memory
+
+* `QEMU allocated memory`
+* `File mapped memory`
+* `Huge pages`
+* `Memory pinning`
+
+### Devices
+
+#### Models
+
+* `virtio`
+  * `blk`
+  * `console`
+  * `crypto`
+  * `pci-net`
+  * `rng-pci`
+  * `scsi`
+	* `virtio`
+	* `vhost`
+  * `9pfs`
+  * `vhost-user-scsi`
+  * `vhost-user-net`
+  * `vhost-user-blk`
+  * `vhost-vsock-pci`
+* `vfio`
+  * `network`
+  * `mediated device`
+  * `storage`
+  * `rdma`
+* `NVDIMM`
+* `TPM`
+  * `vTPM`
+  * `Host TPM passthrough`
+* `SCSI controller`
+* `PCI controller (pci-lite)`
+
+#### Block
+
+* `cdrom`
+* `nvme`
+* `ceph/rbd`
+
+### Guest Image Formats
+
+* `QCOW2`
+* `RAW`
+* `VHD`
+
+### Migration
+
+* `Network based over TLS`
+* `File based` (Local migration)
+
+### Monitoring
+
+* `QMP`
+* `QAPI`
+
+### **To be discussed**
+
+* `64-bit Windows Server (headless)`
+* `qboot`
+* `Graphic Console`
+* `virtio-block-crypto`
+* `QEMU client support as modules`
+  * `iscsi`
+  * `nbd`
+  * `nfs`
+  * `gluster`
+* `RDMA live migration`
+* `SLIRP`
+* `Guest agent`