Point setup at docs/BUILD.md, add repo layout

README.md

@@ -6,6 +6,10 @@ BLE, both on the same Bluetooth stack.
 This is the harder of the two routes. If you want the boring one that works
 first go, see `ps4-lego-bridge` — two boards and a UART between them.
 
+**Build and deploy instructions: [docs/BUILD.md](docs/BUILD.md).** This will not
+compile out of the box — the board package ships the BTstack headers but does
+not put them on the include path, and that has to be fixed first.
+
 ## How it avoids the stack collision
 
 The reason the obvious sketch fails is that Bluepad32 (BTstack) and Legoino
@@ -38,19 +42,14 @@ then `BP32.enableNewBluetoothConnections(true)` opens up for the pad. Bluepad32'
 inquiry and LE scan otherwise run at the same time as our LE create-connection
 and the hub connects unreliably or not at all.
 
-## Setup
+## Layout
 
-1. Preferences → Additional board manager URLs:
-   `https://raw.githubusercontent.com/ricardoquesada/esp32-arduino-lib-builder/master/bluepad32_files/package_esp32_bluepad32_index.json`
-2. Boards Manager → install **esp32_bluepad32**.
-3. Tools → Board → **esp32_bluepad32** → ESP32 Dev Module. Must be the original
-   ESP32 (WROOM/WROVER) — S3/C3/C6/H2 have no Bluetooth Classic.
-4. Partition scheme: **Huge APP**. BTstack with both transports plus the GATT
-   client will not fit the default.
-5. Put your hub addresses in `HUB_ADDR_STR`, flash, watch the serial monitor.
-
-Do not install Legoino or NimBLE-Arduino. If they end up in the build you are
-back to two host stacks.
+```
+ps4_lego_onebrain/ps4_lego_onebrain.ino   the sketch
+docs/BUILD.md                             install, include-path fix, first run
+docs/platform.local.txt                   the include-path override, for restoring
+                                          after a Bluepad32 package update
+```
 
 ## The protocol, in full
 
@@ -81,11 +80,12 @@ Full spec: https://lego.github.io/lego-ble-wireless-protocol-docs/
 
 ## What to expect on the bench
 
-Verified from documentation: the Bluepad32 board-package install, the threading
-contract and `btstack_run_loop_execute_on_main_thread()`, the BTstack GATT
-client call signatures, and the LWP3 message encoding above.
+Verified: the Bluepad32 board-package install, the threading contract and
+`btstack_run_loop_execute_on_main_thread()`, the BTstack GATT client call
+signatures, the LWP3 message encoding above, and — on Jess's machine — that
+package 4.1.0 ships every header this needs under `tools\sdk\esp32\include\`.
 
-Not verified, because it needs your hardware:
+Not verified, because it needs the hardware powered up:
 
 * **Address type.** LEGO's OUI is `90:84:2B`, a public range, so the sketch uses
   `BD_ADDR_TYPE_LE_PUBLIC`. If the connect times out repeatedly with no LE