Update CONTRIBUTING.md to include more details on how to contribute

### Description of the documentation inaccuracy

The current version of CONTRIBUTING.md includes a lot about our philosophy of creating and naming things, but not as much detail as it could about the mechanics of contributing to a specific repo. The contributing guide is linked from repos that don't have their own, so we should add some additional generic info on how to contribute (like pull request workflow, etc). See, for example, https://github.com/alleyinteractive/create-wordpress-project/blob/develop/CONTRIBUTING.md for what this could include. Any links to specific projects should be removed. The resulting documentation should be able to be used for any of our projects.

### Additional Information

_No response_