enh: editor guide -- make toctree / header hierarchy more clear in .

[lwasser]

It would be nice to make the steps in the guide match the steps in the review. Currently the ToC here doesn't lend itself to being a quick reference to use during a review, mostly because a lot of the background information needs to be collapsed into second-tier ToC elements and the titles for the process checklist should probably be changed to match the review stages
Currently it looks like this:

Guide	Tags
Editor Checklist: : Get Started With Leading a Package Review
1. First, tag the submission issue on GitHub	1/editor-checks
2. Respond to the submitter in the GitHub issue	2/seeking-reviewers
3. Identify scientific Python package reviewers
Finding package reviewers
4. Onboard reviewers	3/reviewers-assigned
Editor responsibilities during the review
5. What to do when reviews are in	4/review-in-awaiting-changes
	5/awaiting-reviewer-response
6. How to accept a package into the pyOpenSci ecosystem	6/pyOS-approved
OPTIONAL: Instructions for Submitting to JOSS	7/under-joss-review
	9/joss-approved
Last Steps Before Closing the Review Issue

Which is sort of hard to follow. I think with some simple restructuring we could make each phase in the review match across the docs and the tags - "if i am on step 3/reviewers-assigned, i go to the "3: Reviewers Assigned" section in the docs to see what to do"