Modified installation instructions for OS X

Light Table > LightTable (although I see now that on the website it's Light Table: http://www.lighttable.com/, on github it's LightTable: https://github.com/LightTable/LightTable) Ignore?

Git Config instructions from RailsBridge Installfest (Is there a minimum git --version?)

Heroku, has a new Dashboard, (and couldn't find toolbelt in UI), so removed "found under the Dashboard", but left in Heroku Toolbelt link.
This is a good addition. There's no need to install Git if it's already installed. :)