User: Add more examples for scoped password reset (#409)

When an account has been compromised, then resetting the passwords of users with a particular role or all users can be helpful.

Rather than add new flags to the `user reset-password` command, we can document how to combine with the existing `user list` command instead (see https://make.wordpress.org/cli/handbook/contributions/philosophy/#composability-is-always-a-good-idea). This will then appear when `wp user reset-password --help` is run.

Author: GaryJones

src/User_Command.php

@@ -1114,6 +1114,18 @@ public function import_csv( $args, $assoc_args ) {
 	 *     $ wp user reset-password admin --skip-email --porcelain
 	 *     yV6BP*!d70wg
 	 *
+	 *     # Reset password for all users.
+	 *     $ wp user reset-password $(wp user list --format=ids)
+	 *     Reset password for admin
+	 *     Reset password for editor
+	 *     Reset password for subscriber
+	 *     Success: Passwords reset for 3 users.
+	 *
+	 *     # Reset password for all users with a particular role.
+	 *     $ wp user reset-password $(wp user list --format=ids --role=administrator)
+	 *     Reset password for admin
+	 *     Success: Password reset for 1 user.
+	 *
 	 * @subcommand reset-password
 	 */
 	public function reset_password( $args, $assoc_args ) {