Card devexp_395 Added documentation for STI.

I added the cli docs and I did small flag cleaning:
* unified certain flags (namely `callbackUrl` -> `callbackURL` and `savetempdir` -> `saveTempDir`)
* added `forcePull` and `saveTempDir` to `usage` command, as these make sense there as well

@bparees @csrwng waiting for your comments.
That'll be true when I finish with [this card](https://trello.com/c/pxOTGPlc/416-5-support-arbitrary-images-for-sti-builders). Until then I've decided to write what we have so far. I've added a checkpoint to modify that file in the card.