fix(php-spx): correct documentation to include required SPX_KEY to access the UI

fixes: wardenenv#25 (comment)

Author: SamJUK

configuration/phpspx.md

@@ -32,6 +32,6 @@ Once an environment is started with the `WARDEN_PHP_SPX=1` flag set, all web req
 
 ### Control Panel / Viewer
 
-To view the reports generated by PHP SPX, append `?SPX_UI_URI=/` to the end of your environment url (e.g `https://app.magento2.test/?SPX_UI_URI=/`). 
+To view the reports generated by PHP SPX, append `?SPX_UI_URI=/&SPX_KEY=warden` to the end of your environment url (e.g `https://app.magento2.test/?SPX_UI_URI=/&SPX_KEY=warden`). 
 
 ![Example PHP SPX Control Panel](screenshots/phpspx-control-panel.png)