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.
what's a "source image"?