Fix confusing wording in getting started tutorial

[jackgerrits]

The getting started tutorial is linked to from the start page no matter what package type is installed which is a bit confusing.

The tutorial should make it clear that the command line tool is required and pip install is not sufficient for this tutorial.

[cheng-tan]

In get started module, we should link to vowpal wabbit command line basics and vowpal wabbit python basics based on user's selection.

[kumpera]

Could we improve that module by detecting the current OS of the user and use some query / hyperlink to focus on the right install target (pip vs command line)?