add collection docs to marvin bot index

[zzstoatzz]

First check

• [X] I added a descriptive title to this issue.
• [X] I used the GitHub search to look for a similar issue and didn't find it.
• [X] I searched the Marvin documentation for this feature.

Describe the current behavior

No response

Describe the proposed behavior

scrape w raggy's SitemapLoader

Example Use

No response

Additional context

No response