Add taxonomy description

[LuiseQuoss]

The description of the taxonomy in the datasets is missing. Add a paragraph and point to Lina's Rmarkdowns for an exemplary workflow.

[LuiseQuoss]

@E-O-Conchas and @linamaes I added a first version of the description. Could you please proof-read it and check if this is easy to follow? Are the code-examples too much in this Readme?