Add Pipewire socket permission setup for Flatpak and improve the example path

[jkcdarunday]

Introduction

The script for setting up audio devices for Flatpak uses the pw-link command to connect the microphone's sink to the source. However, this command requires access to the Pipewire socket which is not available in the Steam Flatpak environment by default.

The ff. is the error that occurs when running without the PW socket within the Steam flatpak:

~ ❯❯❯ flatpak run --command=sh com.valvesoftware.Steam
[📦 com.valvesoftware.Steam ~]$ pw-link ALVR-MIC-Sink:monitor_FL ALVR-MIC-Source:input_FL
can't connect: Host is down

Changes

This PR adds a step to add a Flatpak override for the Pipewire socket in order to make the pw-link command work.

It also updates the example path to point to where the previous step asked the user to save the script.