Git user friendlier

From @gabebw's work on https://github.com/railsbridge-boston/railsbridge-vm/pull/12.

Note in the last commit that doesn't show up unless you click it:

    Students should still run the commands to configure git with their real
    name before committing something they will push to Heroku, but this will
    prevent an error message if they're experimenting before they do that.

Note that ~/.ssh has been added here without any special permissions; known_hosts isn't secret information. Should maybe make sure nothing complains about that before merging though.
Great, thanks for changing the host from `railsbridge.com`.