Update API Docs for tips.json

Make sure the `curl` code example works and mention a couple of the gotchyas.
Merge pull request #1110 from twolfson/dev/improve.psycopg2.readme

Updated required package notes
Attempting to use same IF NOT EXISTS logic from add_gittip_user, however psql dislikes doing db creates inside of functions/mulit-line code
Moved to shell script for creating the db
Added gittip db creation to puppet
Added postgresql-contrib to our set of dependencies and `vagrant up` now starts everything locally successfully =D