DOC: Styling guide lacks links to the referenced objects
#### Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/user_guide/style.html

#### Documentation problem

The page lacks links to the referenced objects (`DataFrame`, `Series`, ... but most importantly `Styler`).

#### Suggested fix for documentation

Links should be included. This could either be done using [raw reST cells](https://nbsphinx.readthedocs.io/en/0.8.2/raw-cells.html#reST) (which looks not as nice in the downloadable notebook) or by inserting relative links into the markdown code (which breaks easily).
