DOC: Fix pipe example in the Essential basic functionality page
In our continuous integration we validate that all the examples in the documentation follow PEP-8, and are valid code that can run.

Currently, we're skipping the essential basic functionality page, because the examples showing the `pipe` functionality can't be run, because the variables it uses are not defined. The example can be seen here:
https://github.com/pandas-dev/pandas/blame/master/doc/source/getting_started/basics.rst#L765

What we should do is to replace this example, by a real-world example, where the data is previously created. This way users will be able to run the code, and also will understand better a real-world case where `.pipe()` can be used.

A great resource for understanding `pipe` and to get inspiration for an example is this blog post: https://tomaugspurger.github.io/method-chaining

What needs to be done here is:
- Add a **minimalistic** DataFrame with somehow real-world data.
- Create couple of **one-liner** functions that can be used with pipe and the dataset created, in a meaningful way.
- Make sure that the example is not overcomplicated, and that the data and the functions are so simple that the reader can focus all their attention to understanding `pipe` and method chaining.
- Start validating the code in the file (i.e. remove this line: https://github.com/pandas-dev/pandas/blob/master/setup.cfg#L49)