Ensure src is build when committing

[jorisvandenbossche]

Since it is easy to forget to build the /src files before committing / merging, it would be good to have some checks in place (apart from good documentation):

• pre-commit hook that runs it (I personally have good experience in my python projects now running black in pre-commit hooks, so I think we should set this up and recommend this to contributors). The main concern here is that this doesn't take too long (otherwise it gets annoying to commit). Right now it is fast (on master, less than 2 seconds), but this might become longer in the future if we add more features to the build?
• github action that checks it has run: I suppose we could create configure a github action that eg runs build:production and then checks nothing changed? (or are there other ways to check build:production was run?)

[choldgraf]

+1 to trying out a pre-commit hook

[jorisvandenbossche]

This is now fixed by #154