Update the documentation to reflect the current list of available groups

[lgoettgens]

#52 extended the list of available groups from order up to 4095 to 8191. However, this change is neither reflected in the primgrp manual (https://github.com/gap-packages/primgrp/releases/download/v4.0.0/manual.pdf) nor in the gap documentation (https://docs.gap-system.org/doc/ref/chap50_mj.html)

It would be great to have that fixed until the gap 4.15.0 release (ping @fingolfin).

[ThomasBreuer]

In the same spirit:

The primgrp package contains data and functions about irreducible solvable matrix groups, but I did not find a cross-reference to the irredsol package (http://www.icm.tu-bs.de/~bhoeflin/irredsol).
There is a cross-reference from irredsol to primgrp, and the section "Compatibility with other data libraries" of irredsol explains the relation to primgrp.

(I noticed the problem because of the change of a reference in gap-system/gap#6125.)