I think that most mac users would rather stay as far away from the terminal as possible. You can use command+shift+. to make all invisible files/folders visible in the Finder. Go to your home folder and you should now see the .config folder. Select it and then select Get Info from the File menu (or use command+I). At the bottom it shows permissions. Make sure yours are set to read & write. Do the same for the rstudio folder that is in the .config folder. When done, use command+shift+. again to make the invisible files/folders invisible again.