Double-check and refine docstrings before 3.6.0 release

[bobleesj]

• Use consistent NumPy docstrings style
• Ensure API docs remain clear for new maintainers and users with limited programming experience.

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          maybe we could further refine docstrings in separate issues? @sbillinge

Originally posted by @bobleesj in #228 (comment)

[sbillinge]

would this be a good kind of group hackathon? everyone take a few? Also a learning/teaching experience?

[bobleesj]

Yeah, early next week would be best. I will shift my gears for crystallography for the next 3 days..

I can lead a quick rundown of our group's testing standards and assign members to improve docstrings collaboratively during a call.