Improve the one-line README.md

Bump the version to 0.2.0

Add ggrossman as a contributor and change e-mail to
ggrossman@zendesk.com since eac@zendesk.com no longer valid.
Add length requirements to README

Add License section
Merge pull request #1 from zendesk/ggrossman/update_gemfile_and_readme

Update gemfile and README.md