Index.rst: Update doc to STORE_BEFORE

extension/Documentation/UsersManual/Index.rst

@@ -334,9 +334,11 @@ Store: *RECORD* - R
 Store: *BEFORE* - B
 ^^^^^^^^^^^^^^^^^^^
 
-* Current record loaded in Form withour any modification.
+* Current record loaded in Form without any modification.
 * If r=0, alle values are empty.
 
+This store is handy to compare new and old values of a form.
+
  +------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------+
  | Name                   | Explanation                                                                                                                                      |
  +========================+==================================================================================================================================================+