Administration: Add missing description for "Page title" element of the admin menu array.

Props ajoah, valentinbora, kaitlin414.
Fixes #42911.

git-svn-id: https://develop.svn.wordpress.org/trunk@47434 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/menu.php

@@ -9,13 +9,14 @@
 /**
  * Constructs the admin menu.
  *
- * The elements in the array are :
- *     0: Menu item name
+ * The elements in the array are:
+ *     0: Menu item name.
  *     1: Minimum level or capability required.
- *     2: The URL of the item's file
- *     3: Class
- *     4: ID
- *     5: Icon for top level menu
+ *     2: The URL of the item's file.
+ *     3: Page title.
+ *     4: Classes.
+ *     5: ID.
+ *     6: Icon for top level menu.
  *
  * @global array $menu
  */