add basic ci setup

[jhamman]

No description provided.

[jhamman]

@TomNicholas - this is probably ready to go. The remaining failure is just the pre-commit linter, which I've borrowed from Xarray. Options are:

1. turn it off for now
2. merge with the failure and do a second pr with a big lint-only change log
3. I can run pre-commit as part of this PR and the tests will pass.

[TomNicholas]

Thank you very much @jhamman !

I would prefer option (2), because I want to make sure my linters work locally - I haven't been using them on this project beyond pycharm's default features yet - I put pre-commit in the dependencies aspirationally 😅 If they are the same ones as xarray it should work fine though.

Would you like write access to this repo or shall I just merge it now?

[jhamman]

Happy to just have you merge for now. Go for it when you are ready.