README: complete/simplify instructions for Emacs

Insert complete block to copy-paste into .emacs without modifications (uses "opam config var" to get the path to merlin.el and ocamlmerlin). Loads merlin only when needed. Runs merlin by default on all OCaml files (simplification; the user annoyed by that can clearly see she has only two lines to comment out).

README.md

@@ -114,25 +114,25 @@ Emacs interface
 merlin comes with an emacs interface (file: emacs/merlin.el) that implements a
 minor-mode that is supposed to be used on top of tuareg-mode.
 
-To get it working you only to load the file `emacs/merlin.el' of the distribution.
+If you installed through opam, all you need to do is add the following to your .emacs:
 
-If you installed through opam, a good thing to do is:
+    (push
+     (concat (substring (shell-command-to-string "opam config var share") 0 -1) "/emacs/site-lisp") load-path)
+    (setq merlin-command (concat (substring (shell-command-to-string "opam config var bin") 0 -1) "/ocamlmerlin"))
+    (autoload 'merlin-mode "merlin" "Merlin mode" t)
+    (add-hook 'tuareg-mode-hook 'merlin-mode)
+    (add-hook 'caml-mode-hook 'merlin-mode)
 
-
-    (add-to-list 'load-path "<SHARE_DIR>/emacs/site-lisp/")
-    (require 'merlin)
+If you do not use opam, change the two first expressions above to point to the site-lisp directory containing merlin.el and ocamlmerlin:
 
+    (push "<SHARE_DIR>/emacs/site-lisp" load-path) ; directory containing merlin.el
+    (setq merlin-command "<BIN_DIR>/ocamlmerlin")  ; needed only if ocamlmerlin not already in your PATH
 
 To use it, you will need
 
 - json.el (available by package.el)  
 - auto-complete-mode (optional, available by package.el and the MELPA repository)
 
-Once it is done, to enable merlin in a buffer, just type M-x merlin-mode. If you want merlin to be started on every ML buffer issue:
-
-    (add-hook 'tuareg-mode-hook 'merlin-mode)
-
-
 Features
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