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

android/README.md

@@ -2,7 +2,7 @@
 
 Standalone Android/OpenXR build of the Mario Kart Wii recompilation for Quest 1,
 Quest 2, Quest 3, Quest 3S and Quest Pro, and, as the `steamFrame` flavour, for Valve's Steam
-Frame under Lepton ([docs/steam-frame.md](../docs/steam-frame.md)). The full design, build
+Frame under Lepton (the [README](../README.md#the-android-flavour); the Frame is played with the native SteamOS build). The full design, build
 walkthrough and current status live in [docs/quest-port.md](../docs/quest-port.md); this directory only
 holds the Gradle project, its helper scripts, the game kit tooling
 (`QuestGameKit.psm1`, `Build-QuestGame.ps1`), the on-headset build toolchain