docs for transformers module

[yucongalicechen]

closes #226
didn't add news because previous news already captured the new functionalities
@sbillinge ready for review

[github-actions]

Warning! No news item is found for this PR. If this is a user-facing change/feature/fix,
please add a news item by copying the format from news/TEMPLATE.rst.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7b6ee2e) to head (01e71dc).
Report is 2 commits behind head on main.

Additional details and impacted files

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[bobleesj]

@sbillinge Do we want to use lower_with_underscore for doc .rst files? A bit hard to read diffractionobjectsexample.rst. Not sure about the convention. Did a quick search and appears NumPy is using the lower_with_underscore convention (mostly, not all) https://github.com/numpy/numpy/tree/main/doc/source/reference

[sbillinge]

@sbillinge Do we want to use lower_with_underscore for doc .rst files? A bit hard to read diffractionobjectsexample.rst. Not sure about the convention. Did a quick search and appears NumPy is using the lower_with_underscore convention (mostly, not all) https://github.com/numpy/numpy/tree/main/doc/source/reference

@bobleesj @yucongalicechen yes, let's use this convention. But I don't worry too much for now, I will just merge this.