Set up basic pre-commits

[Anthchirp]

• black (source code formatting)
• syntax validation
• basic flake8 checks

Add an entry point to enable pre-commits if the package is installed
in a dials environment.

You'll have to see how that works in your development environment.
It should be as simple as pip install pre-commit followed by pre-commit install in the repository directory.

[coveralls]

Coverage remained the same at 82.183% when pulling b77c8a5 on precommit into d1f48f7 on master.

[coveralls]

Coverage remained the same at 82.183% when pulling b77c8a5 on precommit into d1f48f7 on master.

[coveralls]

Coverage remained the same at 82.183% when pulling b77c8a5 on precommit into d1f48f7 on master.

[coveralls]

Coverage remained the same at 82.183% when pulling b77c8a5 on precommit into d1f48f7 on master.

[coveralls]

Coverage remained the same at 82.183% when pulling 502e34e on precommit into d1f48f7 on master.

[KarlLevik]

pip install pre-commit and pre-commit install seem to do something, and no errors! So I'll assume this works. We should probably have documentation notes somewhere for developers about these steps.

[Anthchirp]

Good point. I've added some documentation blurb. If you're happy with this then it can go in.

[KarlLevik]

Yes, that looks good! Thank you!