Rework terrain resources in help browser and manual
In part follow-up to #43563. Client help dialog and freeciv-manual aren't particularly well-equipped to nicely display terrain types with many different possible resources, and don't display relative frequencies at all.
alienvalkyrie 
In part follow-up to #43563. Client help dialog and freeciv-manual aren't particularly well-equipped to nicely display terrain types with many different possible resources, and don't display relative frequencies at all.