basis.help.vocabs: include links to parent vocabs in metadata

For vocabs that are children of other vocabs, this gives you easy access
to all of the parent vocabs in the vocab help. It uses the same
breadcrumbing as $vocab-link.

basis/help/vocabs/vocabs.factor

@@ -246,10 +246,12 @@ C: <vocab-author> vocab-author
 
 : describe-metadata ( vocab -- )
     [
-        [ vocab-tags [ "Tags:" swap \ $tags prefix 2array , ] unless-empty ]
-        [ vocab-authors [ "Authors:" swap \ $authors prefix 2array , ] unless-empty ]
-        [ vocab-platforms [ "Platforms:" swap \ $links prefix 2array , ] unless-empty ]
-        tri
+        {
+            [ "." split1-last [ '[ { "Parents:" { $vocab-link _ } } ] call , ] [ drop ] if ]
+            [ vocab-tags [ "Tags:" swap \ $tags prefix 2array , ] unless-empty ]
+            [ vocab-authors [ "Authors:" swap \ $authors prefix 2array , ] unless-empty ]
+            [ vocab-platforms [ "Platforms:" swap \ $links prefix 2array , ] unless-empty ]
+        } cleave
     ] { } make
     [ "Metadata" $heading $table ] unless-empty ;