Since the wireplumber configuration has been moved to /usr/share/pipewire, it
does not makes sense to have a different path for the WIREPLUMBER_CONFIG_DIR
environment variable. Therefore, the WIREPLUMBER_CONFIG_DIR environment variable
has been changed to just be an alias of PIPEWIRE_CONFIG_DIR. Finally, Lua
scripts are now installed under /usr/share/wireplumber/scripts instead of
/usr/share/pipewire/scripts as they are a wireplumber feature only.
* Add information about multiple instances
* Document better how the lua config files work
* Document how lua config files get merged from different places
* Copy over additional documentation for ALSA from pw-media-session
* Fix rst syntax issues