Add contributing guidelines to OneBusAway Android.  After being added to
Github, Github will automatically include a header over the issue editor
saying "Please review the guidelines for contributing to this
repository", with "guidelines for contributing" being hyperlinked to
this markdown file.  See
https://github.com/blog/1184-contributing-guidelines for details.
Merge pull request #80 from CUTR-at-USF/addContributingGuidelines

Add contributing guidelines to OneBusAway Android