doc/org-manual.org: Document the `!' agenda command separately

* doc/org-manual.org (The Agenda Dispatcher): Document the `#' and
`!' agenda commands separately.

doc/org-manual.org

@@ -8455,10 +8455,14 @@ commands:
   to specify the number of context lines for each match, default is
   1.
 
-- {{{kbd(#)}}}, {{{kbd(!)}}} ::
+- {{{kbd(#)}}} ::
 
   Create a list of stuck projects (see [[*Stuck projects]]).
 
+- {{{kbd(!)}}} ::
+
+  Configure the list of stuck projects (see [[*Stuck projects]]).
+
 - {{{kbd(<)}}} ::
 
   #+kindex: < @r{(Agenda dispatcher)}