Add build instructions for the sample to the README

Author: unknownv2

README.md

@@ -5,6 +5,23 @@ Example tool for hooking graphics APIs using [CoreHook](https://github.com/unkno
 
 Based on [Justin Stenning's Direct3DHook](https://github.com/spazzarama/Direct3DHook).
 
+## Requirements
+
+**[Building the sample requires the .NET Core 3.0 SDK, which can be downloaded here.](https://dotnet.microsoft.com/download/dotnet-core/3.0)**
+
+The Direct3D10 and Direct3D11 modules require the .NET Windows Form libraries, which are only available with .NET Core 3.0 and above.
+
+The `deps` folder contains the [`SharpDX.Desktop`](https://github.com/unknownv2/SharpDX.Desktop) library targeting .NET Core 3.0, which is used by the Direct3D10 and Direct3D11 sample modules.
+
+## Building
+
+Clone and build the sample with:
+
+```
+git clone --recursive git://github.com/unknownv2/graphics-hook.git
+cd graphics-hook
+dotnet build
+```
 
 ## References