Fix static method context error in Notices::add()

- Remove static keyword from add() method to allow $this usage
- Resolves "Cannot use '$this' in non-object context" error
- Method now requires instantiation to call: $notices = new Notices(); $notices->add($args);

Fixes #23

Author: alhoseany

src/Admin/Notices.php

@@ -38,7 +38,7 @@ public function __construct() {
 	 * @since <next-version>
 	 * @param array $args The notice arguments.
 	 */
-	public static function add( array $args ) {
+	public function add( array $args ) {
 		$args = wp_parse_args(
 			$args,
 			array(