Add parameter and return descriptions to the `WP_List_Table::get_pagination_arg()` DocBlock.

See #30224.


git-svn-id: https://develop.svn.wordpress.org/trunk@30225 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/class-wp-list-table.php

@@ -247,13 +247,14 @@ class WP_List_Table {
 	}
 
 	/**
-	 * Access the pagination args
+	 * Access the pagination args.
 	 *
 	 * @since 3.1.0
 	 * @access public
 	 *
-	 * @param string $key
-	 * @return int
+	 * @param string $key Pagination argument to retrieve. Common values include 'total_items',
+	 *                    'total_pages', 'per_page', or 'infinite_scroll'.
+	 * @return int Number of items that correspond to the given pagination argument.
 	 */
 	public function get_pagination_arg( $key ) {
 		if ( 'page' == $key )