Added SQLite.rb cheatsheet

Like the title, I added a SQLite.rb cheatsheet from [sqlite3 Cheat Sheet by richardjh - Cheatography.com: Cheat Sheets For Every Occasion]([http://www.cheatography.com/richardjh/cheat-sheets/sqlite3/](http://www.cheatography.com/richardjh/cheat-sheets/sqlite3/)).

Happy cheating!