DOC: fix mask/where docstring alignment note (#61781)
The explanatory paragraph wrongly said that alignment is between `other` and `cond`.  It is between *self* and `cond`; values fall back to *self* for mis-aligned positions.  Update both generic docstring templates so all Series/DataFrame variants inherit the correct wording.

Closes #61781

- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

How do I merge this? 