Add contributing instructions

[stephenmathieson]

I've been trying to get a local version of up running so I can try to better debug (and get a decent understanding of the codebase). However, it's proving to be rather complicated to get my environment setup the way up expects it. So far, I've had to (all trial/error):

• install git-lfs
• install golang/dep
• run dep ensure
• install pointlander/peg
• install jteeuwen/go-bindata
• install golang/mock/mockgen

...and make test is still crashing. Is there any way you could add something to the README (or ./docs/?) which documents all of these steps? I imagine it'd save several people quite a lot of time.

[tj]

FWIW you don't need peg etc unless you want to hack on the log grammar, but I'll try a fresh clone and see if I can add make setup or something, w/ docs.