README.md typos

Corrections:
* "OS" -> **"OS X"**
* "~/Libary/Application Support/Sublime Text 2/Packages/User" -> **"~/Library/Application Support/Sublime Text 2/Packages/User"**
* "git://github.com/chrislongo/TidyJSON.git" -> **"git clone git://github.com/chrislongo/TidyJSON.git"**