help: explain how to access subtopics in internals

mercurial/help.py

@@ -203,7 +203,8 internalstable = sorted([
 
 def internalshelp(ui):
     """Generate the index for the "internals" topic."""
-    lines = []
+    lines = ['To access a subtopic, use "hg help internals.{subtopic-name}"\n',
+             '\n']
     for names, header, doc in internalstable:
         lines.append(' :%s: %s\n' % (names[0], header))
 

tests/test-help.t

@@ -943,6 +943,8 internals topic renders index of availab
   Technical implementation topics
   """""""""""""""""""""""""""""""
   
+      To access a subtopic, use "hg help internals.{subtopic-name}"
+  
        bundles       Bundles
        censor        Censor
        changegroups  Changegroups