improve opam description

Author: gares

coq-hierarchy-builder.opam

@@ -11,8 +11,11 @@ dev-repo: "git+https://github.com/math-comp/hierarchy-builder"
 build: [ make ]
 install: [ make "install" "VFILES=structures.v" ]
 depends: [ "coq-elpi" {>= "1.6" & < "1.9~"} ]
-synopsis: "Hierarchy Builder"
+synopsis: "High level commands to declare and evolve a hierarchy based on packed classes"
 description: """
-High level commands to declare and evolve a hierarchy based on packed classes.
+Hierarchy Builder is a high level language to build hierarchies of algebraic structures and make these
+hierarchies evolve without breaking user code. The key concepts are the ones of factory, builder
+and abbreviation that let the hierarchy developer describe an actual interface for their library.
+Behind that interface the developer can provide appropriate code to ensure retro compatibility.
 """
 tags: [ "logpath:HB" ]