Added a missing <?php tag in a code example opener

Author: pattonwebz

README.md

@@ -29,6 +29,7 @@ require_once get_template_directory() . '/class-wp-bootstrap-navwalker.php';
 If you encounter errors with the above code use a check like this to return clean errors to help diagnose the problem.
 
 ```php
+<?php
 if ( ! file_exists( get_template_directory() . '/class-wp-bootstrap-navwalker.php' ) ) {
 	// file does not exist... return an error.
 	return new WP_Error( 'class-wp-bootstrap-navwalker-missing', __( 'It appears the class-wp-bootstrap-navwalker.php file may be missing.', 'wp-bootstrap-navwalker' ) );
@@ -40,9 +41,9 @@ if ( ! file_exists( get_template_directory() . '/class-wp-bootstrap-navwalker.ph
 You will also need to declare a new menu in your `functions.php` file if one doesn't already exist.
 
 ```php
-	register_nav_menus( array(
-    	'primary' => __( 'Primary Menu', 'THEMENAME' ),
-	) );
+register_nav_menus( array(
+	'primary' => __( 'Primary Menu', 'THEMENAME' ),
+) );
 ```
 ## Usage
 
@@ -125,6 +126,10 @@ You can decide yourself if you want to put up with those drawbacks for the benef
 
 Be sure to set the `echo` argument to FALSE in `the wp_nav_menu()` call when doing this so that the results can be stored instead of echoed to the page.
 
+See also:
+- https://generatewp.com/how-to-use-transients-to-speed-up-wordpress-menus/
+- https://vip-svn.wordpress.com/plugins/cache-nav-menu/cache-nav-menu.php
+
 ### Extras
 
 This script included the ability to use Bootstrap nav link mods in your menus through the WordPress menu UI. Disabled links, dropdown headers and dropdown dividers are supported. Additionally icon support is built-in for Glyphicons and Font Awesome (note: you will need to include the icon stylesheets or assets separately).

class-wp-bootstrap-navwalker.php

@@ -384,7 +384,7 @@ public static function fallback( $args ) {
 		 * Find any custom linkmod or icon classes and store in their holder
 		 * arrays then remove them from the main classes array.
 		 *
-		 * Supported linkmods: .disabled, .dropdown-header, .dropdown-divider
+		 * Supported linkmods: .disabled, .dropdown-header, .dropdown-divider, .sr-only
 		 * Supported iconsets: Font Awesome 4/5, Glypicons
 		 *
 		 * NOTE: This accepts the linkmod and icon arrays by reference.