[ticket/12684] Add extended help for the user:add command

PHPBB3-12684

phpBB/language/en/cli.php

@@ -131,4 +131,7 @@ $lang = array_merge($lang, array(
 // Additional help for commands.
 $lang = array_merge($lang, array(
 	'CLI_HELP_CRON_RUN'			=> $lang['CLI_DESCRIPTION_CRON_RUN'] . ' Optionally you can specify a cron task name to run only the specified cron task.',
+	'CLI_HELP_USER_ADD'			=> 'The <info>%command.name%</info> command adds a new user:
+If this command is run without options, you will be prompted to enter them.
+To optionally send an email to the new user, use the <info>--send-email</info> option.',
 ));

phpBB/phpbb/console/command/user/add.php

@@ -82,6 +82,7 @@ class add extends \phpbb\console\command\command
 		$this
 			->setName('user:add')
 			->setDescription($this->language->lang('CLI_DESCRIPTION_USER_ADD'))
+			->setHelp($this->language->lang('CLI_HELP_USER_ADD'))
 			->addOption(
 				'username',
 				'U',