This can be used as a base as of Git Ignore file for Unity projects:
/[Ll]ibrary/ /[Tt]emp/ /[Oo]bj/ /[Bb]uild/ # Autogenerated VS/MD solution and project files *.csproj *.unityproj *.sln *.suo *.tmp *.user *.userprefs *.pidb *.booproj
If you have lots of Unity projects, you can add/use it as Global Git Ignore file instead.