Add shell of rvm instructions for mac

Prior to this commit, we didn't even have a list of the steps that would
be required for being able to contribute to the website. This commit
adds the shell of the steps required for contributing on a modern-ish
version of Mac OS X.
Add Xcode details

Add Xcode and Command Line Tools details and screenshot.
Better test for empty email
Document postgresql requirement for contributing
Flesh out most of the installation instructions
Add in-page links to the overview
Extract OSX instructions into an OSX file
Fix a typo
More info about what to do with questions
Merge pull request #1 from AndrewLorente/add_contribution_requirements_instructions

Document postgresql requirement for contributing
Improvements to OSX_SETUP.md
Instructions for getting set up on Ubuntu

Tested in an Ubuntu 12.04 VM
Instructions for installing Homebrew.

Homebrew is necessary for installing binary dependencies from rvm.
Merge pull request #1 from jeffweiss/add_contribution_requirements_instructions

Add setup instructions for OSX
Really barebones windows setup instructions
Merge pull request #2 from AndrewLorente/add_contribution_requirements_instructions

Add contribution requirements instructions
Merge branch 'master' of github.com:code-scouts/green_mercury
Install a Node runtime on non-OSX platforms
How to run a dev server
Fix a typo