add contributors.md

Please add a commit adding your name to this file if you like, or add a comment noting that you don't care :P  We have squashed the commit history to nothingness~
- [x] @nsimmons
- [x] @tylermercier
- [x] @kristianpd
- [x] @pushrax 
- [x] @patrickdonovan 

Feel free to ping anyone I may have missed