Fix the installer; start the desktop without the Steam client's environment

install.sh: a comment with an apostrophe inside a single-quoted command
(from the distrobox pin) ended the quote and broke the script at step 1.

The VR launcher started the desktop with the Steam client's environment,
including LD_LIBRARY_PATH to Steam's runtime, whose libavcodec has no
H.264 decoder: VLC in the desktop couldn't play most videos. The session
script now drops the client's variables before starting anything, so apps
use the system's libraries and codecs.

The README and the installer now recommend setting Steam's Sleep after
(When Plugged In and Idle) to Never; Steam suspends the Frame after an
hour otherwise, even while charging.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -28,6 +28,8 @@ You need a Steam Frame with an internet connection, a keyboard (Bluetooth, or th
 
 After the restart, Launch a program → Desktop opens the multi-screen desktop, with its screens arranged around where you're facing. Frametop Display Settings and Frametop Input Settings are in the desktop's application menu, under Settings.
 
+If you work in the desktop for long stretches, stop Steam from putting the headset to sleep while it's plugged in: in Steam, open Settings → Power, and under When Plugged In and Idle set Sleep after to Never. By default Steam suspends the Frame after an hour without input, even while it charges. The displays still turn off a few seconds after you take the headset off.
+
 ### Add a Bluetooth mouse or keyboard
 
 1. Pair it in Steam, under Settings → Bluetooth.