ide-plugin: Update Readme.md to recent changes

README.md

@@ -219,6 +219,13 @@ you to export tests recorded in Selenium IDE to a perl script.
   8. Click 'Ok'
   9. Close Selenium IDE and open it again.
 
+**Note:** The Code generated by this plugin currently assumes that you have firefox 48 or newer + the geckodriver plugin installed. 
+
+If you have an older version of firefox you can adjust the plugin the following way:
+In the options window of selenium IDE (Formats tab) there is a input box called "Header".
+Here you can modify the fixed header code beeing generatd. Change Selenium::Firefox->new();
+according to the firefox init examples shown above in this README.
+
 ## Support and Documentation
 
 There is a mailing list available at