Update readem to better describe capabilities.

Nemesis does a lot more than just changing passwords now.

Change-Id: I41506cfb8ef7635b2e556a80869576588cadab33
Clarify that contributions shouuld go via stock SR mechanisms.

Since Sam isn't maintaining this project any more, and all the
outstanding issues are now in trac, it doesn't really make any sense
to continue requesting that things go via his github clone. Instead,
send things via the standard SR tooling where possible, but allow
GitHub as a fallback just in case any external people want to submit
stuff.

Change-Id: Ica7c0eb042fbc7c7f87e003b3856cfdc76f42682