Add hook doc generation

[jeffpaul]

Is your enhancement related to a problem? Please describe.
There's a reference to sample filters for the Observer in the Article Export section (both in the readme.md and readme.txt files) that links out to a gist outside the repo. Let's add the hook doc generation GitHub Action to the repo and link to that resulting GitHub Pages site from our readme pages.

Describe the solution you'd like

• add hookdoc action
• update the link reference in the Article Export section of readme.md
• update the link reference in the Article Export section of readme.txt

Designs
n/a

Describe alternatives you've considered
keep it as-is?

Additional context
none.