DOC: generate docs for the `Series.dt.isocalendar()` method.
- [ ] 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 an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Screenshots of successfully built docs:

![weekofyear docs linking to isocalendar docs](https://user-images.githubusercontent.com/247555/162068649-857308c5-26ab-49ad-bd80-3fe31ff397f8.png)

![isocalendar docs](https://user-images.githubusercontent.com/247555/162068724-e89c06bd-9fb7-4640-a5d2-a81251accab2.png)


![Series index, showing link to isocalendar docs](https://user-images.githubusercontent.com/247555/162068677-1338417f-5267-4f6c-b7de-2767eed4477f.png)

 hmm can you rebase on master, i think the doc build was borked previous. thanks @tswast something odd on doc CI but your change is orthogonal. @meeseeksdev backport 1.4.x Something went wrong ... Please have a look at my logs.