auditor: add simple comment about repo.auditor and al

Every once in a while, I get confused by what these are. Let us add a comment.

mercurial/localrepo.py

@@ -288,6 +288,8 b' class localrepository(object):'
         self.root = self.wvfs.base
         self.path = self.wvfs.join(".hg")
         self.origroot = path
+        # These auditor are not used by the vfs,
+        # only used when writing this comment: basectx.match
         self.auditor = pathutil.pathauditor(self.root, self._checknested)
         self.nofsauditor = pathutil.pathauditor(self.root, self._checknested,
                                                 realfs=False)