- Add the code-spell pre-commit hook.
- Correct the spelling errors it found.

So you can insert mnpw between some other system and the plugin.

I think it's OK now that the functionality is there, the usability is
there, it's well(-ish) tested.

If someone wants the wheel to use as a library.

Document the current state of the development. Remove proselint
pre-commit hook as it complains on the usage info and I can't ignore
specific lines and the README is the only file that I want proselint to
lint so out it goes. Add a better description for dry-run (now that I
decided what I meant by it).