some tiny care for the Sponsoring page

[Federico Bruni]

During a recent discussion I suggested few ideas to make the sponsoring 
page more visible:
https://lists.gnu.org/archive/html/lilypond-devel/2015-10/msg00131.html

But after reading this old thread:
https://lists.gnu.org/archive/html/lilypond-devel/2012-11/msg00131.html

I realize that I don't want to discuss, so I suggest only these two 
simple changes:

- Download page: add a Note box with a link to the Sponsoring page 
(which is hidden under Community), so that casual users, not subscribed 
to lilypond-user, may know about this possibility.

- Sponsoring page: update the statistics (reminder for Phil), see: 
https://sourceforge.net/p/testlilyissues/issues/2086/