Include Dunfell (Azure#47)

Author: micahl

README.md

@@ -14,6 +14,7 @@ Use the branch of `meta-iotedge` corresponding to your Yocto release:
 * [Thud](https://github.com/Azure/meta-iotedge/tree/thud) - `git clone -b thud https://github.com/Azure/meta-iotedge.git`
 * [Warrior](https://github.com/Azure/meta-iotedge/tree/warrior) - `git clone -b warrior https://github.com/Azure/meta-iotedge.git`
 * [Zeus](https://github.com/Azure/meta-iotedge/tree/zeus) - `git clone -b zeus https://github.com/Azure/meta-iotedge.git`
+* [Dunfell](https://github.com/Azure/meta-iotedge/tree/dunfell) - `git clone -b dunfell https://github.com/Azure/meta-iotedge.git`
 
 In almost all cases, you should not use the `master` branch of `meta-iotedge` in your image.