Documenting the release process

[otoolep]

@zmedico -- I got following question on the rqlite Slack:

"I found in the pyrqlite and sqlalchemy-rqlite repositories that last month an enhancement related with ping/do_ping were merged but there is no new tag/release for those libraries after it.
Do you plan to release it soon? I think that is something we can benefit from."

and

"I'm not very familiar with the process but I guess the python packages will be updated once the tag is created?
https://pypi.org/project/pyrqlite/
https://pypi.org/project/sqlalchemy-rqlite/"

If we tag pyrqlite and sqlalchemy-rqlite, we have to do something explicit in PyPi too, right? I have an account there, did you publish sqlalchemy-rqlite? I should document the release process.