Improvements to contributing guide

[banesullivan]

Here is a draft of some improvements to the contributing guide for you to run with. Would you please update this to your liking and make sure it has clear instructions for local development and testing?

For https://github.com/pyOpenSci/software-submission/issues/138

[raphaelquast]

Thank you very much for opening this PR! Highly appreciated! I'll report back once it's finished.

[raphaelquast]

Hey @banesullivan Both CONTRIBUTING.md and the associated Contribution Guide in the docs are now updated to include infos on tests etc.

• I've decided to only provide a quick-overview in CONTRIBUTING.md and link to the docs for more extensive explanations.
• I've switched the base to the dev branch so I can already use the MySt syntax

Please let me know if you are OK with the changes!

If yes, I'll merge this PR into dev so it will be included in the next release!

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (3313346) 76.71% compared to head (6b0717f) 76.71%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #213 +/- ## ======================================= Coverage 76.71% 76.71% ======================================= Files 23 23 Lines 11155 11155 ======================================= + Hits 8557 8558 +1 + Misses 2598 2597 -1 ```

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[raphaelquast]

Thanks for your support and your prompt feedback!