add psalm:strict to the readme

Signed-off-by: Simon L. <szaimen@e.mail.de>

php/README.md

@@ -56,6 +56,7 @@ Note: You can restart the server by preceding the command with other environment
 |-----------------------------------------|----------------------------------------|
 | `composer run dev`                      | Starts the development server          |
 | `composer run psalm`                    | Run Psalm static analysis              |
+| `composer run psalm:strict`             | Run Psalm static analysis strict       |
 | `composer run psalm:update-baseline`    | Run Psalm with `--update-baseline` arg |
 | `composer run lint`                     | Run PHP Syntax check                   |
 | `composer run lint:twig`                | Run Twig Syntax check                  |