Update dotnet-projects.md
Update dotnet-projects.md

Added Coding4fun toolkit to the list of OSS projects
690486439/dotnet,richlander/dotnet,velyo/dotnet,Microsoft/dotnet,BruceForstall/dotnet,punker76/dotnet,punker76/dotnet,Microsoft/dotnet,richlander/dotnet,BruceForstall/dotnet,velyo/dotnet