Add example code to download a dataset to the data card

[hagenw]

It might be convinient to have the line of code needed to download a dataset included on the data card.

E.g. for emodb v1.4.1, the code would look like this:

db = audb.load("emodb", version="1.4.1")

At the moment, a user would need to copy and paste the title and version of a dataset in two steps in order to write the command in the command line. That would be improved by adding example code.

I would locate the example code before or directly after the dataset overview table on the data card.