docs(python): Add a couple of docstring examples to Series methods

[r-brink]

Related to: Add missing docstring examples #13161

Includes the following examples from the provided csv file

https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.abs.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.cbrt.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.exp.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.log.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.log10.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.log1p.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.skew.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.sqrt.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.is_sorted.html
https://pola-rs.github.io/polars/py-polars/html/reference/series/api/polars.Series.null_count.html

[MarcoGorelli]

Nice! Only super minor comment would be to include an example for log with a different base, but not a blocker (and can be done later!)

[stinodego]

Looks great, thanks!

For future examples, you may want to include some values that are of particular interest to that method, like you've done for abs (include some negative values). For example, sqrt could've been 1, 2, and -9 or something. Or log could include math.e and 10 and showcase the default and base=10.

In any case, good job and this can be merged!