lang/ocaml: add merlin-eldoc type and doc on hover display

This displays the type and documentation of thing under point
and highlights occurrences automatically when idle. Could be achieved by appropriate use of
keyboard shortcuts already set up by this module.

However `merlin-eldoc` can also display the expected type of function call parameters,
which merlin itself wouldn't.

Signed-off-by: Edwin Török <edwin@etorok.net>

modules/lang/ocaml/config.el

@@ -53,6 +53,10 @@
     (add-hook 'merlin-mode-hook #'+ocaml|init-flycheck))
 
 
+  (def-package! merlin-eldoc
+    :hook (merlin-mode . merlin-eldoc-setup))
+
+
   (def-package! utop
     :when (featurep! :feature eval)
     :defer t  ; loaded by hook below