Fold the Steam Frame guide into the README, with a quick start

docs/steam-frame.md is gone. The README now opens with a quick start that
goes from the disc to playing (emulation setup, disc extraction, the
container build, installing with Frame Control, updating), and carries what
the guide held that a player or contributor needs: recommended settings, the
Frame controller map, known issues, troubleshooting (log lines, the pacing
line, crash backtraces), building on the Frame or with Docker (including
Unraid's qemu registration), how the native build works and why the Android
flavour cannot show a picture. Links to the old guide point at the README.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019HBRGKTE1GnN2ah8gcZKr3

docs/quest-port.md

@@ -823,7 +823,7 @@ Android facts this design rests on, all measured on a Quest 3:
   application ID and storage, but select the appropriate CPU baseline (one
   `headsetCpus` map in `app/build.gradle.kts`), manifest and launcher
   behavior. `steamFrame` is Valve's Steam Frame under Lepton, SteamOS's
-  Android layer; see `docs/steam-frame.md`.
+  Android layer, where it cannot show a picture; see the README, The Android flavour.
   `app/src/main/cpp/CMakeLists.txt` adds the repository's `runtime/` as a
   subdirectory with those Android choices and builds both game kit probes
   (the Retro Rewind one only when the translation includes the mod), which
@@ -852,7 +852,7 @@ powershell -ExecutionPolicy Bypass -File android/Build-Quest.ps1 -Headset quest1
 powershell -ExecutionPolicy Bypass -File android/Build-QuestGame.ps1 -Install         # your game, against that kit, into Import (or WheelWizard VR's Build for Quest)
 powershell -ExecutionPolicy Bypass -File android/Build-QuestGame.ps1 -Product retro_rewind -Mod <RetroRewind6> -Install  # the mod and its pack (needs translate-mod output with --retro-wfc-payload)
 powershell -ExecutionPolicy Bypass -File android/Build-QuestGame.ps1 -Headset quest1 -Install  # game package from the Quest 1 kit
-powershell -ExecutionPolicy Bypass -File android/Build-Quest.ps1 -Headset frame       # Steam Frame flavour (docs/steam-frame.md)
+powershell -ExecutionPolicy Bypass -File android/Build-Quest.ps1 -Headset frame       # Steam Frame flavour (README, The Android flavour)
 adb push MarioKart.iso /sdcard/Download/                                               # then Select disc image in the launcher
 ```