Add alternate ways to find projects to static Contributing page

This is a content addition to the Contributing page so that ways to find projects persist once the December 2013 campaign begins (and the temporary notice goes away).

![24pullrequests_addwaystofindprojects-2](https://f.cloud.github.com/assets/226228/1556950/b932b594-4ef5-11e3-8711-c12069b409c7.png)