ENH: (Automatically) provide links to examples and the userguide within the documentation
#### Is your feature request related to a problem?

While Panda's documentation is stellar, it often only answers the "how" of a specific function, not the "when" or "why". This makes it hard to know what a specific function should be used for and what common usecases are.

#### Describe the solution you'd like

Matplotlib and Sklear both have a very nice solution to this problem, where they automatically (I think) include links in the end of documentation pages towards examples that use that specific function, and to relevant places in the user guide.


