Add GitHub PHP syntax highlighting to example

README.mdown

@@ -6,6 +6,9 @@ Monolog - Logging for PHP 5.3
 Usage
 -----
 
+```php
+<?php
+
 use Monolog\Logger;
 use Monolog\Handler\StreamHandler;
 
@@ -16,6 +19,7 @@ Usage
 // add records to the log
 $log->addWarning('Foo');
 $log->addError('Bar');
+```
 
 Core Concepts
 -------------