Added Visual Studio .suo files

[vvolkgang]

*.suo files are binary, user specific files generated by Visual Studio with some user configuration information, thus, don't need to be versioned.

[arcresu]

Thanks for this! These rules are covered in VisualStudio.gitignore; do you think that it's worth duplicating them here in Unity.gitignore?

[vvolkgang]

Yes, for the sake of commodity and "newbie proofing".

1. VisualStudio.gitignore it's huge and 95% of it covers cases that don't apply to Unity3D development
2. As Unity is one of the few (hell, only?) places I know one ever ignores project files, the .suo file is the only one missing and in my opinion, inexperienced developers will think that that file is required for some unkown reason (because all of the other "VisualStudio" related files were already ignored).

[arcresu]

That makes sense; thanks for explaining! ✨