config/graphical-session/xorg: fix grep pattern to detect modesetting…

… driver

src/config/graphical-session/xorg.md

@@ -88,7 +88,7 @@ EndSection
 and restart Xorg. Verify that the configuration has been picked up with:
 
 ```
-$ grep -m1 '(II) modeset([0-9]+):' /var/log/Xorg.0.log
+$ grep -E -m1 '\(II\) modeset\([0-9]+\):' /var/log/Xorg.0.log
 ```
 
 If there is a match, modesetting is being used.