doc: describe full help document hierarchy to create a valid link in HTML

For example, ":hg:`help config.default-push`" creates an invalid link
to "hgrc.5.html#default-push" in HTML, but ":hg:`help
config.paths.default-push`" creates a valid link to
"hgrc.5.html#paths".

hgext/histedit.py

@@ -901,7 +901,7 b' def histedit(ui, repo, *freeargs, **opts'
     - Specify ANCESTOR directly
 
     - Use --outgoing -- it will be the first linear changeset not
-      included in destination. (See :hg:`help config.default-push`)
+      included in destination. (See :hg:`help config.paths.default-push`)
 
     - Otherwise, the value from the "histedit.defaultrev" config option
       is used as a revset to select the base revision when ANCESTOR is not

mercurial/help/config.txt

@@ -800,7 +800,7 b' variables it is passed are listed with n'
 ``outgoing``
   Run after sending changes from local repository to another. ID of
   first changeset sent is in ``$HG_NODE``. Source of operation is in
-  ``$HG_SOURCE``; Also see :hg:`help config.preoutgoing` hook.
+  ``$HG_SOURCE``; Also see :hg:`help config.hooks.preoutgoing` hook.
 
 ``post-<command>``
   Run after successful invocations of the associated command. The
@@ -881,11 +881,11 b' variables it is passed are listed with n'
 ``txnclose``
   Run after any repository transaction has been committed. At this
   point, the transaction can no longer be rolled back. The hook will run
-  after the lock is released. See :hg:`help config.pretxnclose` docs for
+  after the lock is released. See :hg:`help config.hooks.pretxnclose` docs for
   details about available variables.
 
 ``txnabort``
-  Run when a transaction is aborted. See :hg:`help config.pretxnclose`
+  Run when a transaction is aborted. See :hg:`help config.hooks.pretxnclose`
   docs for details about available variables.
 
 ``pretxnchangegroup``