README: fix flathub remote

Thanks to sindreoy in #19 for pointing this out

README.md

@@ -11,7 +11,7 @@ It is unlikely that Flathub would accept a proprietary application like the Jage
 You can install it by adding the remote and installing it with the following commands:
 
 ```bash
-flatpak remote-add --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
+flatpak remote-add --user --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
 flatpak remote-add --user --if-not-exists JagexLauncher https://jagexlauncher.flatpak.mcswain.dev/JagexLauncher.flatpakrepo
 # Required for 32-bit compatibility. Jagex Launcher is 32-bit.
 flatpak install --user flathub org.freedesktop.Platform.Compat.i386/x86_64/23.08