remote: Usage message is a bit confusing

E.g., it would be very helpful if it actually said which options are required; which options are mutually exclusive or override each other, etc. Right now it looks like the usage message was written for a predecessor of stprov, and it does not accurately reflect the current implementation.

I'd like to avoid making this into a "let's refactor stprov's CLI interface" and see what low hanging fruit updates we can do just to the usage message so that it is more helpful compared to today.