FireWatch: About this data

**Describe the task**
Adds 'About this data' to FireWatch

**Acceptance Criteria**
- [ ] describes data sources/models used
- [ ] how calculations are done?

**Additional context**
- Add any other context about the task here.
- Or here

No file, test, or entry point is identified in the issue. First locate the FireWatch data sources, models, and calculation documentation, then determine where an “About this data” section belongs. Done means the section describes the sources and models used and explains how calculations are performed.

Written by the indexing model from the issue text.