Update `--help` output and sponsors automatically

[rootwork]

See https://github.com/premail/premail/blob/main/.github/workflows/update-readme.yml for how this is being done in the internal premail docs.

This is blocked on the new release being pushed to npm, because the GitHub action will need to install premail in order to run the command.

[rootwork]

Unblocked.

[rootwork]

The first part of this issue is now being done with yarn run premail-output-update; see https://github.com/premail/website/blob/main/.github/workflows/deploy.yml#L26

So now we just need to add the sponsor update from https://github.com/premail/premail/blob/main/.github/workflows/update-readme.yml#L31-L35