add justification of the relation with hyp{o,er}nyms.

[kohlhase]

Something like

semigroup
 * hyponyms (transitive)
    monoid since module monoids includes semigroup
    group since module group includes monoids includes semigroup.

this is somewhat like the explanations in flatsearch. BTW, all the "includes" should be clickable and give us the relevant part of the module graph with the path highlighted.