Minor fix

README.md

@@ -18,6 +18,6 @@ Run
 
 The easiest way to Pico is using [the built-in web server on PHP](<http://php.net/manual/en/features.commandline.webserver.php>).
 
-    php -S 0.0.0.0:8080 ./
+    $ php -S 0.0.0.0:8080 ./
 
 Pico will be accessible from <http://localhost:8080>.