README: rewrite for frame-beta-3 and the update modes

Restructure the README around what a player does: choose where to build
(PC or the Frame), install, update, play, then settings, controls,
known issues and troubleshooting. Building on a server and by hand move
under "Other ways to build", and the upstream and credits notes are
merged into "What comes from where" and a short Credits section that
points at CREDITS.md.

Updating now shows the curl form of --update, which works without a
local copy of the script; the in-game Updates tab; and the one full
install needed when coming from frame-beta-2. Manual steps use the
frame-beta-3 tag, the install options are a table, and the Troubleshooting
section covers in-game update failures. Links to the old "The Android
flavour" section now point at "How it works".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Axv1Y43Lu5a5rSSLUyU5BB

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 (the [README](../README.md#the-android-flavour); the Frame is played with the native SteamOS build). The full design, build
+Frame under Lepton (the [README](../README.md#how-it-works); 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