[DOC] Create release docs

[ericmjl]

This issue is to remind myself to create docs for doing releases.

Quoting from @hectormz:

---

🤙🤙 @ericmjl I think in the checklist after bumpversion we can add:

git push <remote> <branch> --follow-tags

which according to this SO answer is the "sane" way to push tags as it

It pushes both commits and only tags that are both:

    - annotated
    - reachable (an ancestor) from the pushed commits

I don't completely understand the differences between annotated and unannotated flags, but I tested our bumpversion tags, and they qualify.

Originally posted by @hectormz in https://github.com/ericmjl/pyjanitor/issues/643#issuecomment-595498724

---

[ericmjl]

@hectormz I just realized I sort of kind of addressed this issue in the Wiki: https://github.com/ericmjl/pyjanitor/wiki/How-to-cut-a-new-release

This is a new addition, I only recently got to this.

Still going to leave this one open because I think the release protocol should be documented in the docs once it gets finalized - including links to how to get the necessary credentials.