do not reference project/product home page

Currently we have 5 different places where you can look for castellum:

• Product home page: https://castellum.mpib.berlin
• Project home page: https://www.mpib-berlin.mpg.de/research-data/castellum
• Source code: https://git.mpib-berlin.mpg.de/castellum/castellum/
• End-user documentation: https://castellum.mpib.berlin/documentation/
• Contact email: castellum@mpib-berlin.mpg.de

My proposal:

• both "source code" and "end-user documentation" are self contained, i.e. the respective audience finds all relevant information in a single place
• all 4 websites link to "source code" and "end-user documentation" and "contact email"
• "product home page" and "project home page" merely serve as entry points and are not linked to from the other places.

What do you think?