Add hook for documentation

[dangunter]

Currently we provide a hook to provide a diagram

We could also provide a hook to add description in text. This could include:

• [required] main description text
• [optional] link to page in watertap docs (could be specified as a relative path from technical reference root, or perhaps by an id)
• [optional] other URLs for references, related software, etc. {name: (url, description)}