Add documentation of catalogues

[tijmenbaarda]

The project members have prepared good documentation about the contents and peculiarities of all our catalogues. This information will be important for the users of the VRE (as discussed on 2023-08-08). Where should we put this documentation, and how do we pass this on to the VRE?

[jgonggrijp]

Maybe just an HTML page somewhere, so we can link to it from the VRE? If it also needs to be machine-readable, we could write it in RDFa, which is human-readable HTML and machine-readable RDF at the same time. If it doesn't need to be machine-readable, we could write it in Markdown instead.