Revise fill-human-* doc strings

[dgr]

Point user at fill-human-el for details on opts.

Closes issue #637.

Please complete and include the following checklist:

• [x ] I have read CONTRIBUTING and the Etaoin Developer Guide.

• [x ] This PR corresponds to an issue that the Etaoin maintainers have agreed to address.

• [x ] This PR contains test(s) to protect against future regressions (NOT NEEDED)

• [x ] I have updated CHANGELOG.adoc with a description of the addressed issue. (NOT NEEDED)

[lread]

Thanks @dgr!

[lread]

Oh. This did not close 637. Ah. The syntax that GitHub recognizes for Closes/Fixes etc is here: https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword

Will close #637

[dgr]

Sorry about that. Thanks.

[lread]

No problem at all, @dgr! Thanks for your continued interest and contributions to Etaoin!