add parallel testing example to README

[mcleanmds]

Based of recent experience getting Django parallel testing working with a redis db, it may be useful to document the approach.

Happy for any feedback/changes.

If this is outside the scope of what the README should cover, please reject.

[WisdomPill]

Hello @mcleanmds!

First and foremost, thanks for the contribution.
Can you provide a test case for this?

I would also point to those tests in the docs.

This is mainly to keep track of any api changes that might happen in django in the future

[WisdomPill]

Add it to the test suite please