Convert to README.md, update content.

README.md

@@ -0,0 +1,48 @@
+# DHCPLite
+
+> A small, simple, configuration-free DHCP server for Windows.
+
+## Background
+
+In 2001, I wrote DHCPLite to unblock development scenarios between Windows and prototype hardware we were developing on.
+I came up with the simplest DHCP implementation possible and took all the shortcuts I could - but it was enough to get the job done!
+Since then, I've heard from other teams using DHCPLite for scenarios of their own.
+And recently, I was asked by some [IoT](https://en.wikipedia.org/wiki/Internet_of_Things) devs to share DHCPLite with that community.
+So I dug up the code, cleaned it up a bit, got it compiling with the latest toolset, and am sharing the result here.
+I hope you find it useful!
+
+## Overview
+
+For those times when you need a DHCP server but don't have the right hardware or software: there's DHCPLite!
+DHCPLite is a small, simple, configuration-free [DHCP (Dynamic Host Configuration Protocol)](https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol) server that runs on Windows and will serve IP addresses to any [RFC2131](http://www.ietf.org/rfc/rfc2131.txt)/[2132](http://www.ietf.org/rfc/rfc2132.txt) compliant device.
+
+> **Warning!**
+> Do **NOT** run DHCPLite when connected to a network that already has a DHCP server on it.
+> DHCPLite was *not* designed to cooperate with other DHCP servers and *will* cause serious problems.
+
+## Implementation Notes
+
+- DHCPLite was designed to work alongside [APIPA (Automatic Private IP Addressing (Auto-IP))](https://en.wikipedia.org/wiki/Link-local_address).
+  If the host machine acquired its IP address in this manner, DHCPLite will not serve a new address to the host machine.
+  (Other machines on the network will be able to obtain IP addresses from DHCPLite.)
+- DHCPLite determines the range of addresses it will hand out based on the current IP address and subnet mask of the non-loopback network interface of the machine on which it is running.
+  In the case of a host configured by APIPA, this means an address of the form 169.254.x.x and a range of over 65,000 available addresses.
+  In the case of a host with a static IP address, the address and range can be changed by altering the static IP address and subnet mask settings on the machine.
+- Once it has assigned an IP address to a specific client, DHCPLite will *always* assign that same address to the client (until DHCPLite is shutdown and restarted).
+  This means it is possible to exhaust the available address space with either a large number of machines or a small address space.
+- In an attempt to mitigate possible misconfiguration problems, DHCPLite hands out address leases that are valid for only 1 hour.
+  Lease renewal is supported, so this should not be a problem for long-running scenarios (as long as DHCPLite is running to issue renewals).
+- DHCPLite requires the IP Helper API (implemented in `iphlpapi.dll`).
+
+## Unsupported Scenarios
+
+- Multi-homed host machines (i.e., host machines with more than one active network interface).
+  Because the [WinSock API](https://en.wikipedia.org/wiki/Winsock) does not allow an application to disable routing of outbound datagrams (sockopt `SO_DONTROUTE` can be silently ignored), DHCPLite would not be able to ensure all outgoing datagrams used the intended interface.
+
+## Unsupported DHCP Features
+
+- `DHCPDECLINE`, `DHCPRELEASE`, and `DHCPINFORM` messages. (See notes above.)
+- Requested IP Address option. (Related to notes above.)
+- Unicast to hardware address.
+  Because DHCPLite is a Windows client application, it does not have access to the underlying network drivers that would allow it to accomplish this.
+  Instead, broadcast messages are used and other DHCP clients are relied upon to ignore spurious DHCP messages.