Update wiki documentation

[webhart]

The Fair Data Points mentioned in the wiki documentation are offline:
https://github.com/FAIRDataTeam/FAIRDataPoint/wiki/Active-FAIRDataPoints

[MarekSuchanek]

The wiki documentation is kept just in "archived" state without any changes (see here, it guides you to use https://github.com/FAIRDataTeam/FAIRDataPoint-Spec.

@kburger maybe we should make this more explicit on each page?

[luizbonino]

The specifications of the FAIR Data Point can be found at https://specs.fairdatapoint.org.
For the list of FDPs, we developed the index service where FDPs are registered and their metadata indexed. Whoever would like to host and maintain an FDP index can deploy their own index. For demonstration purposes, we maintain the https://home.fairdatapoint.org .