Added reference documentation

[onel]

First batch of files with adding reference documentation to some files.
This is a test run to see if the style + content is helpful.

It follows the google docstring style but if the methods have types added it does not also add the Args: Returns: because that would be duplicate information. And also at risk of becoming out of sync.

Feedback more than welcomed.

#8930

[chenmoneygithub]

Thanks for the PR!

Let's make sure every PR handles relevant files, for this specific one we can keep simba_utils.py only.