Remove reference to Aurget

Aurget has been deprecated: https://github.com/pbrisbin/aurget/issues/66
As such I would recommend removing it from the install instructions.

README.md

@@ -201,7 +201,8 @@ ffsend --help
 ```bash
 yay -S ffsend
 # or
-aurget -S ffsend-bin
+aurto add ffsend
+sudo pacman -S ffsend
 # or using any other AUR helper
 
 ffsend --help