docs: improve flatpak start commands (#3264)

packaging/linux/flatpak/dev.lizardbyte.app.Sunshine.metainfo.xml

@@ -32,7 +32,7 @@
     <p>flatpak run --command=additional-install.sh @PROJECT_FQDN@</p>
     <p>NOTE: Sunshine uses a self-signed certificate. The web browser will report it as not secure, but it is safe.</p>
     <p>NOTE: KMS Grab (Optional)</p>
-    <p>sudo -i PULSE_SERVER=unix:$(pactl info | awk '/Server String/{print$3}') flatpak run @PROJECT_FQDN@</p>
+    <p>sudo -i PULSE_SERVER=unix:/run/user/$(id -u $whoami)/pulse/native flatpak run @PROJECT_FQDN@</p>
   </description>
 
   <releases>