Merge pull request #25 from Azure/ewertons/deprecation

Update readme.md to inform deprecation

Author: ewertons

README.md

@@ -1,5 +1,16 @@
 #### Azure IoT Protocol MQTT Library source files
 
+> ### Stop! Before you proceed:
+>
+> _This Arduino Library is deprecated._
+>
+> _It is kept here for **reference only** and should not be used for any new development._
+>
+> _If you’re looking for an Arduino Library you should use the new version: [aka.ms/arduino](https://aka.ms/arduino)_
+>
+>_You can find more information about it in this [IoT Tech Community blog post](https://techcommunity.microsoft.com/t5/internet-of-things-blog/arduino-library-for-azure-iot/ba-p/3034455)._
+>
+
 This is the location of the Arduino-specific source files for the
 [AzureIoTProtocol_MQTT Arduino published library](https://github.com/Azure/azure-iot-arduino-protocol-mqtt).