doctr configure instruction.

[Carreau]

Feedback from user using it for the first time:

• remind that doctr-deploy should be run from root of repo (or it may not find the encrypted key).

[gforsyth]

Thanks @Carreau ! Yeah, I've actually forgotten this myself a time or two. It shouldn't be too hard to detect if we're in a git repo and if so, to then warn if we aren't at the root of it.