Cleaning up doc strings

[drewoldag]

This is work that accrues to rail issue 22 (https://github.com/LSSTDESC/rail/issues/22)

Multiple people are contributing to this PR. Generally we've broken up the rail_base repo by top level directories. In the following list, if there's a check box, it means that the directory has already been looked over.

• [ ] cli
• [ ] core (finished algo_utils, common_param, data)
• [x] creation (#78)
• [ ] estimation (partially finished with CatEstimator)
• [x] evaluation
• [x] example_data - not really any doc strings here.
• [x] stages - no doc strings here

Code Quality

• [ ] My code follows the code style of this project
• [ ] I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• [ ] My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• [ ] Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (263b2a6) 96.96% compared to head (ca3aad5) 96.96%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #75 +/- ## ======================================= Coverage 96.96% 96.96% ======================================= Files 32 32 Lines 1714 1714 ======================================= Hits 1662 1662 Misses 52 52 ```

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