Add some documentation for generating heatmaps...Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/non-clustered-heatmaps-and-flipping.gmi
* Add some documentation on generating the heatmaps, that would be
useful for the end user.
Document how to run tests...* doc/testing.org:
- Update how Mechanical Robs works. Python replaced Ruby as
the testing tool
- Add section that describes how to run unit tests