Document minimal VS installation for samples (#794)

samples/prerequisites.md

@@ -1,23 +1,50 @@
-If you're new to .NET make sure to visit the [official starting page](http://dotnet.github.io). It will guide you through installing pre-requisites and building your first app.
-If you're already familiar with .NET make sure you've [downloaded and installed the .NET 5 SDK](https://www.microsoft.com/net/download/core).
+If you're new to .NET, make sure to visit the [official starting page](http://dotnet.github.io). It will guide you through installing pre-requisites and building your first app.
+If you're already familiar with .NET, make sure you've [downloaded and installed the .NET 5 SDK](https://www.microsoft.com/net/download/core).
 
-The following pre-requisites need to be installed for building .NET 5 projects with CoreRT:
+The following pre-requisites need to be installed for building .NET 5 projects with CoreRT.
 
 # Windows
 
-* Install [Visual Studio 2019](https://visualstudio.microsoft.com/vs/community/), including Visual C++ support.
+* Install [Visual Studio 2019](https://visualstudio.microsoft.com/vs/community/), including Desktop development with C++ workload.
+
+## Advanced Alternative: Minimum Visual C++ Build Tools Installation
+If you wish to save disk space and do not need Visual Studio IDE, you may use the [Build Tools](https://visualstudio.microsoft.com/downloads/#build-tools-for-visual-studio-2019)
+edition instead. First download the [bootstrapper](https://aka.ms/vs/16/release/vs_buildtools.exe) executable.
+On Windows 10 version 1803 or later you may use the `curl` tool:
+
+```cmd
+curl -L https://aka.ms/vs/16/release/vs_buildtools.exe -o vs_buildtools.exe
+```
+
+Then launch the bootstrapper passing the installation path and the two required components (requires elevation):
+```cmd
+vs_buildtools.exe --installPath C:\VS2019 --add Microsoft.VisualStudio.Component.VC.Tools.x86.x64 Microsoft.VisualStudio.Component.Windows10SDK.19041 --passive --norestart --nocache
+```
+Alternatively you may launch the bootstrapper without any options and use Visual Studio Installer UI to enable C++ x64/x86 build tools and Windows 10 SDK individual components.
+
+Notes:
+- You may skip the `Windows10SDK.19041` component if you already have Windows 10 SDK installed on your machine.
+- To target Windows ARM64, you need to add the `Microsoft.VisualStudio.Component.VC.Tools.ARM64` (C++ ARM64 build tools) component instead.
+- The `--installPath` option affects Build Tools installation only. Visual Studio Installer is always installed into
+the `%ProgramFiles(x86)%\Microsoft Visual Studio\Installer` directory.
+
+If you have no `vcruntime140.dll` library installed in your `%SystemRoot%\System32` directory, you also need to install Visual C++ 2019 Redistributable package, which ILCompiler depends on:
+- [vc_redist.x64.exe](https://aka.ms/vs/16/release/vc_redist.x64.exe) (for x64 machine)
+- [vc_redist.arm64.exe](https://aka.ms/vs/16/release/vc_redist.arm64.exe) (for ARM64 machine)
 
 # Fedora (31+)
 
-Tested on Fedora 31, will most likely work on lower versions, too.
+* Install `clang` and developer packages for libraries that .NET Core depends on:
 
 ```sh
 sudo dnf install clang zlib-devel krb5-libs krb5-devel ncurses-compat-libs
 ```
 
+This was tested on Fedora 31, but will most likely work on lower versions too.
+
 # Ubuntu (16.04+)
 
-* Install clang and developer packages for libraries that .NET Core depends on.
+* Install `clang` and developer packages for libraries that .NET Core depends on:
 
 ```sh
 sudo apt-get install clang zlib1g-dev libkrb5-dev