update documentation after every push

[d-morrison]

see https://github.com/r-lib/actions/tree/v2/examples#document-package

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

[d-morrison]

doesn't work yet; filing bug report

[d-morrison]

The github actions workflow I'm adding here seems to be a little buggy (I filed an issue here) but still worth adding to main now. Ideally, it will never run because we all consistently remember to run document() frequently; but if we forget, this workflow will catch it and run it for us; then we just need to add another commit to get the other workflows to run again.

[d-morrison]

Looks like this workflow also has trouble when merging main into an out-of-date PR branch (bug report filed here). Still worth adding this workflow to main; we can work around these bugs, and forgetting to document() has been a recurring problem that I'd really like to automate.

[d-morrison]

closing for now; #186 is a simpler option without bugs to work around.