org-install.el: Enhance warning

* org-install.el: Enhance warning.

Thanks to Simon Thum for requesting this.

lisp/org-install.el

@@ -1,8 +1,10 @@
-;;; org-install.el --- autogenerated file, do not edit
+;;; org-install.el --- backward compatibility file for obsolete configuration
 ;;
 ;;; Code:
 (warn "The file org-install is obsolete.
-Please change your configuration to (require 'org) instead.")
+It is provided here so that (require 'org-install) does not
+trigger an error for users with obsolete Emacs configuration.
+You can safely remove (require 'org-install) from your config.")
 
 (provide 'org-install)