Update credits in README
Update credits in README

* Split up license section
* Add "About thoughtbot" section

thoughtbot/neat,jessieay/neat,craftsmen/neat,Martskin/neat,smithdamen/neat,thoughtbot/neat,greyhwndz/neat,2metres/neat,setie/neat,nickg33/neat,kennethormandy/straight-up,craftsmen/neat,craftsmen/neat,bgreg/neat,thoughtbot/neat,chriseppstein/neat,bahtiyara/neat