Restructure documentation for better usability

Commenting for credit attribution

Changes are in PR https://git.drupalcode.org/project/codit_batch_operations/-/merge_reques...

Thankyou @davidmpickett for this amazing work. I do appreciate all you put into this. And props for putting it in a MR!!

This one is going to have to percolate in my head for a bit.
Right now I keep all the documentation in the one file because it feeds

1. The main page in the git repo
2. The project page on Drupal.org
3. The internal help link that appears directly in Drupal

I do it like this because Drupal has built-in helpers that allow me to connect all three. And I do it that way across the many modules I maintain, mainly to keep me sane (not having to maintain different documentation locations).

There is really no tooling right now to connect multiple markdown files in both the help page and the module's project page. The existing tooling oddly does not digest links well. ie Either links work on the project page, but not the help page, or vice versa.

I need to give some more thought to this for a bit to see if I can come up with a way to make this work smoothly on all three use cases. Ultimately, yours is the better way, so I want to get there as soon as I figure out how.