docs: Shorter README, with a Steam Machine section

How it works moved to TECHNICAL.md, problems to TROUBLESHOOTING.md.

TROUBLESHOOTING.md

@@ -0,0 +1,57 @@
+# Troubleshooting
+
+See [TECHNICAL.md](TECHNICAL.md) for how each part works.
+
+## Gaming mode shows a black screen or keeps restarting
+
+Press **Ctrl+Alt+F3**, log in with your username and password, and run:
+
+```bash
+sudo /usr/lib/steamos/steam-set-session plasma.desktop && sudo systemctl restart display-manager
+```
+
+That takes you back to the desktop. Gamescope sessions that fail to start are
+restarted right away (`Relogin=true`), which is why it can loop.
+
+## Something is set up wrong
+
+Run the wizard again and press `a` in the menu to re-apply everything that's
+on (also useful after a CachyOS update). To undo a part, untick it.
+
+## The LED bar on the Steam Machine stays dark
+
+Restart once more; a freshly installed driver often needs a reboot. The menu
+shows per kernel whether the LED driver is built, and whether it's loaded.
+Still dark:
+
+```bash
+dkms status
+ls -l /sys/class/leds/valve-leds*/
+sudo dmesg | grep -i valve
+cat /var/lib/dkms/leds-valve-dkms/0.1/build/make.log
+journalctl --user -b | grep -i led
+```
+
+## The Steam Machine still reboots when I shut it down
+
+Check that the pinned kernel is installed and running:
+
+```bash
+uname -r                                   # should be 7.1.6-1-cachyos
+pacman -Q linux-cachyos linux-cachyos-headers
+grep '^IgnorePkg' /etc/pacman.conf         # should list both packages
+```
+
+Not running it yet? Restart. Not installed? Run the wizard and make sure
+**Pin the kernel** under Steam Machine support is ticked. If you have more
+kernels installed (e.g. the LTS kernel), pick `linux-cachyos` in the boot menu.
+
+## The kernel pin can't download or verify the kernel
+
+The wizard tries this repo's `kernel-7.1.6-1` release, then the CachyOS
+archive and mirror. A file that fails its checksum or CachyOS signature is
+deleted, so running the wizard again downloads it once more. Offline? Put
+the four files from the
+[kernel-7.1.6-1 release](https://github.com/theupriser/steamify-cachyos/releases/tag/kernel-7.1.6-1)
+in `/var/cache/steamify/kernel` and run it again.
+