Updated Fetching pages with WebDriver (markdown)

Fetching-pages-with-WebDriver.md

@@ -44,6 +44,7 @@ The URL for the WebDriver interface is set with the `WEBDRIVER_URL` environment
 
 Known to work with RaspberryPi-4 Use the `seleniarm/standalone-chromium:4.0.0-20211213` as `image:`. Note that this currently only supports the 64-bit version of Raspbian OS.
 
+- It's good to set the ENV var `FETCH_WORKERS` to a low value like 2 or 3, because maybe having 10 sessions of chrome open might be a bit too heavy on your rPi
 
 ## There's a few things left todo