Add documentation for __serialize and __unserialize

src/Collections/ImmutableCollection.php

@@ -168,11 +168,23 @@ class ImmutableCollection implements IImmutableCollection {
         throw new ImmutableException();
     }
 
+    /**
+     * List of properties to {@see https://www.php.net/manual/function.serialize.php serialize}
+     *
+     * @return array[] List of properties to {@see https://www.php.net/manual/function.serialize.php serialize}
+     */
     public function __serialize (): array {
         return [
             'elements' => $this->elements,
         ];
     }
+    /**
+     * {@see https://www.php.net/manual/function.unserialize.php Unserialize} from the list of serialized properties
+     *
+     * @param array $data The list of serialized properties
+     *
+     * @return void
+     */
     public function __unserialize (array $data): void {
         $this->_initialize($data['elements']);
     }