Update documentation

Author: justafish

README.md

@@ -26,7 +26,9 @@ ddev nightwatch --tag core
 
 ## Nightwatch Examples
 
-You can watch Nightwatch running in real time at https://drupal.ddev.site:7900 for Chrome and https://drupal.ddev.site:7901 for Firefox. The password is "secret".
+You can watch Nightwatch running in real time at https://drupal.ddev.site:7900
+for Chrome and https://drupal.ddev.site:7901 for Firefox. The password is
+"secret". YMMV using Firefox as core tests don't currently run on it.
 
 Only core tests
 ```