bisect: refer directly to bisect() revset predicate in help

We have specific syntax for displaying the help text for a particular
revset predicate, so let's refer directly to the bisect() revset in
the verbose bisect help. It seems likely that the user doesn't care
about other revsets at that point, so they will probably not miss the
text about the other revset predicates.

mercurial/commands.py

@@ -823,7 +823,7 b' def bisect(ui, repo, rev=None, extra=Non'
 
           hg log --graph -r "bisect(range)"
 
-      See :hg:`help revsets` for more about the `bisect()` keyword.
+      See :hg:`help revisions.bisect` for more about the `bisect()` predicate.
 
     Returns 0 on success.
     """