[docs] Add build instructions

[skip ci]

README.md

@@ -12,6 +12,15 @@ We use [Git Submodules](https://git-scm.com/book/en/v2/Git-Tools-Submodules)
 [Git LFS](https://git-lfs.github.com/), so make sure you have that installed if
 you want to get all files.
 
+## Building and installation
+
+If you want to use the emulator, you can either [build it from
+sources](docs/build.md) (that's slow), [use partially prebuilt
+artifacts](docs/artifacts.md) (that's fast and recommended if you want to make
+changes; however, you still need to have Docker and Visual Studio installed) or
+just [use prebuilt binaries](https://github.com/ipasimulator/ipasim/releases)
+(recommended if you don't want to make changes).
+
 ## Directory structure
 
 - [`deps`](deps) contains third-party dependencies (mostly as Git submodules because

docs/README.md

@@ -24,6 +24,9 @@
 
 ## Building
 
+In this section, we describe some advanced building scenarios. Basic building
+instructions [are available elsewhere](build.md).
+
 Install and run Docker for Windows (tested with version `18.06.1-ce-win73`),
 enable Windows containers,
 [increase maximum container disk size](https://docs.microsoft.com/en-us/visualstudio/install/build-tools-container?view=vs-2017#step-4-expand-maximum-container-disk-size)

docs/artifacts.md

@@ -0,0 +1,21 @@
+# Prebuilt artifacts
+
+Following [our build instructions](build.md) step-by-step can be a very
+time-consuming task. To speed up the process, prebuilt artifacts are available.
+
+- Instead of running `docker-compose build`, you can pull container
+  [`ipasim/build`](https://hub.docker.com/r/ipasim/build):
+
+  ```bash
+  docker pull ipasim/build
+  ```
+
+- Instead of running `./scripts/build.ps1`, you can pull container
+  [`ipasim/artifacts`](https://hub.docker.com/r/ipasim/artifacts) and then start
+  the container like this:
+
+  ```bash
+  docker pull ipasim/artifacts
+  docker tag ipasim/artifacts ipasim/build
+  docker-compose run --name ipasim ipasim powershell
+  ```

docs/build.md

@@ -0,0 +1,34 @@
+# Build instructions
+
+## Prerequisites
+
+1. Install [Docker Desktop for
+   Windows](https://hub.docker.com/editions/community/docker-ce-desktop-windows).
+2. [Switch to Windows
+   containers](https://docs.docker.com/docker-for-windows/#switch-between-windows-and-linux-containers).
+3. Install [Visual Studio](https://visualstudio.microsoft.com/) (around version
+   2019).
+
+## Build process
+
+Inside the repository root, run:
+
+```bash
+docker-compose build
+docker-compose run --name ipasim ipasim powershell
+```
+
+Once inside the built container, run:
+
+```bash
+./scripts/build.ps1
+./scripts/extract.ps1 Release
+```
+
+Finally, open `src/IpaSimulator/IpaSimApp.sln` in Visual Studio and run it (in
+configuration `Release`). Alternatively, you can use `Debug` configuration, but
+then you have to execute command `./scripts/extract.ps1 Debug` instead of the
+one mentioned above.
+
+If you don't want to build everything from scratch, you can [use prebuilt
+artifacts](artifacts.md).