Add "this may take a while" message

Add a message for the long-running task of installing the new flatpak
repo, which can take several minutes depending on the user's internet
speed.

ublue-firstboot

@@ -28,7 +28,7 @@ if [ "$?" != 0 ] ; then
 fi
 echo "5"
 
-echo "# Replacing Fedora Flatpaks with Flathub Ones"
+echo "# Replacing Fedora Flatpaks with Flathub Ones (this may take a while)"
 /usr/bin/flatpak install --user --noninteractive org.gnome.Platform//43
 /usr/bin/flatpak install --user --noninteractive --reinstall flathub $(flatpak list --app-runtime=org.fedoraproject.Platform --columns=application | tail -n +1 )
 if [ "$?" != 0 ] ; then
@@ -130,4 +130,4 @@ touch "$HOME"/.config/ublue/firstboot-done
 if [ "$?" != 0 ] ; then
         zenity --error \
           --text="Firstboot Configuration Error"
-fi
+fi