Creation docstrings

[OliviaLynn]

Problem & Solution Description (including issue #)

For LSSTDESC/rail#22 (creation docstrings only)

Made this branch before seeing Drew's dedicated branch for the issue, sorry Drew

Code Quality

• [x] My code follows the code style of this project
• [x] 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

[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 (8cfc16f) 97.17%. Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #78 +/- ## ========================================== + Coverage 96.96% 97.17% +0.21% ========================================== Files 32 32 Lines 1714 1736 +22 ========================================== + Hits 1662 1687 +25 + Misses 52 49 -3 ```

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