add in root and check command

Yes its an instruction to the user. We could call setenv, but a) I don't like changing envs and b) it won't persist. Having this persist so you can run `fig` from any directory, including the working code directory.

https://github.com/mozilla/marketplace-docs/pull/38/files#diff-5d4db6049a4d8219f7904c20b4409366R60