Document SDK change

README.md

@@ -48,8 +48,8 @@ How to build
 ------------
 
 Windows:
-- Install Visual Studio (documented version: 16.3) with the following components:
-  - Workload ".NET Desktop Development". This includes by default .NET Framework 4.8 SDK and the .NET Framework 4.7.2 targeting pack, as well as the [.NET Core 3.0 SDK](https://dotnet.microsoft.com/download/dotnet-core/3.0) (ILSpy.csproj targets .NET 4.7.2, and ILSpy.sln uses SDK-style projects).
+- Install Visual Studio (documented version: 16.4) with the following components:
+  - Workload ".NET Desktop Development". This includes by default .NET Framework 4.8 SDK and the .NET Framework 4.7.2 targeting pack, as well as the [.NET Core 3.1 SDK](https://dotnet.microsoft.com/download/dotnet-core/3.1) (ILSpy.csproj targets .NET 4.7.2, and ILSpy.sln uses SDK-style projects).
   - Workload "Visual Studio extension development" (ILSpy.sln contains a VS extension project)
   - Individual Component "MSVC v142 - VS 2019 C++ x64/x86 build tools (v14.23)" (or similar)
     - The VC++ toolset is optional; if present it is used for `editbin.exe` to modify the stack size used by ILSpy.exe from 1MB to 16MB, because the decompiler makes heavy use of recursion, where small stack sizes lead to problems in very complex methods.
@@ -60,11 +60,13 @@ Windows:
   - Run project "ILSpy" for the ILSpy UI
   - Use the Visual Studio "Test Explorer" to see/run the tests
 
-**Note:** Visual Studio 16.3 and later include a version of the .NET Core SDK that is managed by the Visual Studio installer, once you update to 16.4 it may get upgraded to version 3.1. Please note that ILSpy is not compatible with the .NET Core 3.1 SDK and Visual Studio will refuse to load some projects in the solution. If this problem occurs, please manually install the .NET Core 3.0 SDK from [here](https://dotnet.microsoft.com/download/dotnet-core/3.0).
+**Note:** Visual Studio 16.3 and later include a version of the .NET Core SDK that is managed by the Visual Studio installer - once you update, it may get upgraded too.
+Please note that ILSpy is only compatible with the .NET Core 3.1 SDK and Visual Studio will refuse to load some projects in the solution (and unit tests will fail). 
+If this problem occurs, please manually install the .NET Core 3.1 SDK from [here](https://dotnet.microsoft.com/download/dotnet-core/3.1).
 
 Unix / Mac:
 - Make sure .NET Core 2.1 LTS Runtime is installed (you can get it here: https://get.dot.net).
-- Make sure [.NET Core 3.0 SDK](https://dotnet.microsoft.com/download/dotnet-core/3.0) is installed.
+- Make sure [.NET Core 3.1 SDK](https://dotnet.microsoft.com/download/dotnet-core/3.1) is installed.
 - Check out the repository using git.
 - Execute `git submodule update --init --recursive` to download the ILSpy-Tests submodule (used by some test cases).
 - Use `dotnet build Frontends.sln` to build the non-Windows flavors of ILSpy (.NET Core Global Tool and PowerShell Core).