Issue #22317: Document the action parameter in ArgumentParser.add_subparsers() docs.

Patch by Mike Short.

Doc/library/argparse.rst

@@ -1521,12 +1521,15 @@ Sub-commands
    * parser_class - class which will be used to create sub-parser instances, by
      default the class of the current parser (e.g. ArgumentParser)
 
-   * dest - name of the attribute under which sub-command name will be
+   * action_ - the basic type of action to be taken when this argument is
+     encountered at the command line
+
+   * dest_ - name of the attribute under which sub-command name will be
      stored; by default None and no value is stored
 
-   * help - help for sub-parser group in help output, by default None
+   * help_ - help for sub-parser group in help output, by default None
 
-   * metavar - string presenting available sub-commands in help; by default it
+   * metavar_ - string presenting available sub-commands in help; by default it
      is None and presents sub-commands in form {cmd1, cmd2, ..}
 
    Some example usage::