org.el: Minor update of docstrings.

(org-open-at-mouse): Point to the docstring of `org-open-file'
for more details.
(org-open-file): Mention `org-link-frame-setup' in the
docstring.

Thanks to Reiner Steib for pointing at this.

lisp/org.el

@@ -9294,7 +9294,8 @@ This is still an experimental function, your mileage may vary."
   (org-open-at-point 'in-emacs))
 
 (defun org-open-at-mouse (ev)
-  "Open file link or URL at mouse."
+  "Open file link or URL at mouse.
+See the docstring of `org-open-file' for details."
   (interactive "e")
   (mouse-set-point ev)
   (if (eq major-mode 'org-agenda-mode)
@@ -9957,6 +9958,10 @@ Optional LINE specifies a line to go to, optional SEARCH a string
 to search for.  If LINE or SEARCH is given, the file will be
 opened in Emacs, unless an entry from org-file-apps that makes
 use of groups in a regexp matches.
+
+If you want to change the way frames are used when following a
+link, please customize `org-link-frame-setup'.
+
 If the file does not exist, an error is thrown."
   (let* ((file (if (equal path "")
 		   buffer-file-name