Adding .gitattributes

This will help in a scenario where someone uses a git submodule on this tree. 

Your windows line endings in the XSDs will cause anyone wishing to convert linux line endings to cause the submodule to become dirty automatically when you submodule update due to the line ending conversions.

You might want to add this file to all your repositories to help when someone wants to submodule it.

This way line endings are preserved and not converted when submoduling.