Fixed typo in org-mobile-index-file docstring.

lisp/org-mobile.el

@@ -133,7 +133,7 @@ been appended to the file given here.  This file should be in
 This should not be changed, because MobileOrg assumes this name.")
 
 (defcustom org-mobile-index-file "index.org"
-  "The index file with inks to all Org files that should be loaded by MobileOrg.
+  "The index file with links to all Org files that should be loaded by MobileOrg.
 Relative to `org-mobile-directory'.  The Address field in the MobileOrg setup
 should point to this file."
   :group 'org-mobile