Updated README containing a summary and directing towards the website for further information.
Removed sponsor text in favour of the donation information on the website.
Merge pull request #1161 from slygamer/readme

Updated README containing a summary...
[WINRT] - Added an optional Delegate to Customize the Game class after it is created
Merge pull request #1168 from tpastor/develop3d

[WINRT] - Added an optional Delegate to Customize the Game class after i...
Merge branch 'develop3d' of https://github.com/mono/MonoGame into develop3d