Manual.rst: update doc for altsql.

Documentation/Manual.rst

@@ -812,10 +812,11 @@ QFQ Keywords (Bodytext)
  +-------------------+---------------------------------------------------------------------------------+
  | <level>.twig      | Twig Template                                                                   |
  +-------------------+---------------------------------------------------------------------------------+
- | <level>.althead   | If <level>.sql is empty, these token will be rendered.                          |
+ | <level>.althead   | If <level>.sql has no rows selected (empty), these token will be rendered.      |
  +-------------------+---------------------------------------------------------------------------------+
- | <level>.altsql    | If <level>.sql is empty, these query will be fired. No sub queries.             |
- |                   | Shown after `althead`                                                           |
+ | <level>.altsql    | If <level>.sql has no rows selected (empty) or affected (delete, update, insert)|
+ |                   | the <altsql> will be fired. Note: Sub queries of <level> are not fired, even if |
+ |                   | <altsql> selects some rows.                                                     |
  +-------------------+---------------------------------------------------------------------------------+
  | <level>.content   | | *show* (default): content of current and sub level are directly shown.        |
  |                   | | *hide*: content of current and sub levels are stored and not shown.           |