Add Database creation steps to documentation

I tried to run the application on my Mac running OS X 10.10 (Yosemite) and I got the following error:

play.api.Configuration$$anon$1: Configuration error[Cannot connect to database [default]]

I created the db directory and then created the database using sqlite3 command then ran the script that was provided.  I added the steps I took to get the database created to the documentation.