Mention beta version of PlatformIO is required

README.md

@@ -57,6 +57,12 @@ platformio run -e $ESP_BOARD --target upload
 
 Of course make sure to substitute `nodemcuv2` with the board that you're using.
 
+**Note that currently you'll need to use the beta version of PlatformIO.**  To install with pip:
+
+```
+pip install -U https://github.com/platformio/platformio-core/archive/develop.zip
+```
+
 You can find pre-compiled firmware images on the [releases](https://github.com/sidoh/esp8266_milight_hub/releases).
 
 #### Configure WiFi