Add infrastructure policy

See merge request !1

Draft based on James's and my conversation last Friday.

https://github.com/OpenTechStrategies/docs/commit/63400bdbf90258e

Specifically, these sections:

* Code Review Happens Before Merge
* The "Obvious Fix" Exception
* No surprise rebasing

This starts on issue #2.  I'm not marking that issue as resolved yet,
though, because DEPLOYMENT.md needs more material in it first.

Thanks to Will Hawkins for spotting this in commit d52a580d.

As discussed with James Vasile.