Update README with instructions for DrupalKernel bridge.

Author: Kent Richards

README.md

@@ -1,5 +1,7 @@
 # PHP-PM HttpKernel Adapter
 
+## Overview
+
 This is a fork of PHP-PM's HttpKernel adapter for integrating Drupal with PHP-PM (therefore, also with ReactPHP).
 
 See:
@@ -10,7 +12,7 @@ The code is in alpha -- very experimental.  Last tested against `drupal-8.0.2`.
 
 View / report issues at https://github.com/kentr/php-pm-drupal/issues.
 
-### Setup
+### Setup / Usage
 
   1. Install Drupal.
 
@@ -40,3 +42,26 @@ start \
 --bridge=httpKernel \
 --bootstrap=PHPPM\\Bootstraps\\Drupal
 ```
+
+## DrupalKernel bridge
+
+`\PHPPM\Bridges\DrupalKernel` extends `\PHPPM\Bridges\HttpKernel` to populate various request meta-variables specified by CGI/1.1 (RFC 3875)[http://www.faqs.org/rfcs/rfc3875.html].
+
+### Setup / Usage
+
+  1. Install as described above.
+
+  2. Include the environment variables and the `--bridge` option in the php-pm start command:
+
+Example:
+
+```bash
+SCRIPT_NAME=/index.php \
+REQUEST_METHOD=GET \
+SERVER_NAME=localhost \
+SERVER_ADDRESS=127.0.0.1 \
+DOCUMENT_ROOT=/var/www/html \
+/var/www/html/vendor/bin/ppm start /var/www/html \
+--bridge=PHPPM\\Bridges\\DrupalKernel \
+--bootstrap=PHPPM\\Bootstraps\\Drupal
+```