Hi daanvink
The readme.txt file should be in the download. You should also be able to open it from within FARR by going to the Options window, selecting the 'Plugins and Updates' category, pressing the 'Click to Examine and Configure Plugins..' button, selecting the FARR Most Recently Used plugin and finally pressing the 'View Plugin Readme/Help File'.
As an example look at the FarrMostRecentlyUsed.config file in the FarrMostRecentlyUsed plugin directory. Don't make changes in there but create a similar looking file called FarrMostRecentlyUsed.user with your configuration instead.