Migrate contributing and test writing docs from wiki to sphinx

[djhoese]

This PR migrates the contributor's guide from the Wiki as well as the documentation on writing tests and puts them in the sphinx docs under a new Developer's Guide.

I think I'd still like to migrate the installation instructions just to make sure the language between what was on the wiki and what was put in the sphinx docs are similar and cover the same use cases.

[djhoese]

@ameraner I updated the installation instructions with the bundle information I used in the Wiki. The conda-based installation instructions you/ask added likely aren't very relevant anymore since, correct me if I'm wrong, they were intended more for testing among ASK and EUMETSAT developers, right? If we assume this installation document is for users then we could probably just replace this with a conda-forge based conda install uwsift command, right?

Right now the old developer install instructions basically said "install sift using conda, uninstall the uwsift package, then install it from git source". This has the downside that if new dependencies are needed for unreleased functionality a new contributor won't know that until things fail. Perhaps we should point developers/contributors to a conda YAML file to create their environment. Thoughts?

[djhoese]

Once this is merged I will update the contributing wiki page to point to the RTD site (if not remove the wiki page completely).

[ameraner]

Regarding your point on the developer installation and the requirements. I agree, having a visible requirements.yaml for this purpose would be nice! In principle it would be the same as the requirements in setup.py, no? Is it possible to have a unified yaml file and point setup.py to it?

[djhoese]

Regarding your point on the developer installation and the requirements. I agree, having a visible requirements.yaml for this purpose would be nice! In principle it would be the same as the requirements in setup.py, no? Is it possible to have a unified yaml file and point setup.py to it?

No. The YAML is used by conda, setup.py is only used by pip. There is a chance package names are different and we're actually running into that with the readthedocs stuff where if you do pip install -e . in a conda environment that already has pyqt=5.x installed it will try to install pyqt5 from PyPI because the package names are different.

[djhoese]

pre-commit.ci autofix

[djhoese]

I migrated the installation instructions from the wiki. I think this is good to go for now.