add "donate" link to "About" navigation bar

I think that a Donate link should be added to the "About" navigation
bar. I realize that it is redundant - but people expect navigation
cues on the left-hand side of pages. (see Nielson studies, Tufte, etc)

This idea came to me after I clicked through 4-5 pages without
finding the link. I'm giving out elephant pins for SPI donations, and
felt a bit silly that I didn't see 'DONATE' at the top of the page.
The text is just low-contrast enough to stay hidden if you're relying
on the navigation menu on the left side of the page to find what
you're looking for.

-selena