DOC: See also missing links in GroupBy.apply(), GroupBy.pipe() 

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.GroupBy.pipe.html#pandas.core.groupby.GroupBy.pipe

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.core.groupby.GroupBy.pipe.html#pandas.core.groupby.GroupBy.apply

#### Problem description

GroupBy.apply() and GroupBy.pipe() have missing links in their See also section. Might be other missing links in other functions of GroupBy.

Specifically, the links that are not working are Series.apply, DataFrame.apply, Series.pipe, DataFrame.pipe

#### Expected Output

Links should take you to named functions
