mention the polkit dependency when using elogind or systemd-logind

Bug: https://github.com/djpohly/dwl/issues/138

README.md

@@ -51,7 +51,7 @@ As in the dwm community, we encourage users to share patches they have created.
 
 ## Running dwl
 
-dwl can be run on any of the backends supported by wlroots. This means you can run it as a separate window inside either an X11 or Wayland session, as well as directly from a VT console. Depending on your distro's setup, you may need to add your user to the `video` and `input` groups before you can run dwl on a VT.
+dwl can be run on any of the backends supported by wlroots. This means you can run it as a separate window inside either an X11 or Wayland session, as well as directly from a VT console. Depending on your distro's setup, you may need to add your user to the `video` and `input` groups before you can run dwl on a VT. If you are using `elogind` or `systemd-logind` you need to install polkit; otherwise you need to add yourself in the `seat` group and enable/start the seatd daemon.
 
 When dwl is run with no arguments, it will launch the server and begin handling any shortcuts configured in `config.h`. There is no status bar or other decoration initially; these are instead clients that can be run within the Wayland session.