Add code to disable the "Open Recent" menu if it contains 0 items.
Merge pull request #3244 from dneelyep/Issue3122

Add code to disable the "Open Recent" menu in Pipeline.exe if it contains 0 items.
Added new tutorial link.
Added more detailed instructions on editing docs.
Tweaked the forking instructions a bit.
Merge pull request #3247 from SickheadGames/docs2

Small Doc Update
Merge branch 'develop' of https://github.com/mono/MonoGame into skywave_6