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.
I guess this is where you say the prior image has to exist, you might use image instead of build.  it's not really clear what a "prior build" really means.