Replace C# port with maintained fork (#5922)

Readme.md

@@ -44,7 +44,7 @@ Start by reading [our build instructions](https://github.com/assimp/assimp/blob/
 ### Ports ###
 * [Android](port/AndroidJNI/README.md)
 * [Python](port/PyAssimp/README.md)
-* [.NET](https://bitbucket.org/Starnick/assimpnet/src/master/)
+* [.NET](https://github.com/Saalvage/AssimpNetter)
 * [Pascal](port/AssimpPascal/Readme.md)
 * [Javascript (Alpha)](https://github.com/makc/assimp2json)
 * [Javascript/Node.js Interface](https://github.com/kovacsv/assimpjs)