Link to Google Groups archives and subscriptions

It's not obvious how to get from that email address to subscribing.
Make it more obvious.
Wordsmithing

Attempt to reduce some language, and make others more concrete.
setup.py to pip: setup.py is broken by OpenStack

And it doesn't look like there is a disposition to fix that upstream
anytime soon:
https://github.com/wal-e/wal-e/issues/65#issuecomment-30197249