Add readme.md listing breaking changes doc chronologically (#56019)

Author: jcouv

docs/compilers/CSharp/readme.md

@@ -0,0 +1,10 @@
+Breaking changes (newest release on top):
+
+- [.NET 6 and Visual Studio 2022](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20DotNet%206.md)
+- [Minor releases following .NET 5 and Visual Studio 2019 version 16.9](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20post%20DotNet%205.md)
+- [.NET 5 and Visual Studio 2019 version 16.9](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20DotNet%205.md)
+- [Minor releases following Visual Studio 2019 version 16.0](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20post%20VS2019.md)
+- [Visual Studio 2019 version 16.0](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20VS2019.md)
+- [Minor releases following Visual Studio 2017 version 15.0](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20post%20VS2017.md)
+- [Visual Studio 2017 version 15.0](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20VS2017.md)
+- [Visual Studio 2015 version 14.0](https://github.com/dotnet/roslyn/blob/main/docs/compilers/CSharp/Compiler%20Breaking%20Changes%20-%20VS2015.md)