cubicweb-comment #2941127 Document basic usage [validation pending]

Explain how to link and use the comment cube in another cube (e.g. insert comments in a view of an entity).

prioritynormal
typeenhancement
done in1.10.0
load0.200
load left0.000
closed by#64c4eb1e9279 [doc] Document basic usage of the cube (closes #2941127).
patch[doc] Document basic usage of the cube [applied]