added platform-io install hint

Author: 256dpi

README.md

@@ -7,6 +7,8 @@ This library bundles the [lwmqtt](https://github.com/256dpi/lwmqtt) MQTT 3.1.1 c
 
 Download the latest version from the [release](https://github.com/256dpi/arduino-mqtt/releases) section. Or even better use the builtin Library Manager in the Arduino IDE and search for "MQTT".
 
+The library is also available on [PlatformIO](https://platformio.org/lib/show/617/MQTT). You can install it by running: `pio lib install "MQTT"`. 
+
 ## Compatibility
 
 The following examples show how you can use the library with various Arduino compatible hardware: