Add README for Pico Audio extras setup

examples/pico_audio/README.md

@@ -0,0 +1,24 @@
+# Pico Audio Pack Demo
+
+This demo requires the `pico-extras` repository to compile - https://github.com/raspberrypi/pico-extras.
+
+You should clone it alongside `pico-sdk` and `pimoroni-pico`:
+
+```
+git clone https://github.com/raspberrypi/pico-extras
+```
+
+And adjust your `cmake` configure command to include the path:
+
+```
+cmake .. -DPICO_SDK_POST_LIST_DIRS=/path/to/pico-extras
+```
+
+If you're using Visual Studio Code you can add this to `settings.json`:
+
+```json
+{
+    "cmake.configureSettings": {"PICO_SDK_POST_LIST_DIRS": "/path/to/pico-extras"}
+}
+```
+