Added ONNX converter docker image to readme (#87)

Author: alexstelea

README.md

@@ -19,6 +19,7 @@
 ## End-to-end tutorials
 
 * [Docker image for Caffe2/PyTorch tutorials](pytorch_caffe2_docker.md)
+* [Caffe/Keras/CoreML Docker Converter Image](https://hub.docker.com/r/microsoft/onnxconverter/)
 * [Converting SuperResolution model from PyTorch to Caffe2 and deploying on mobile device](tutorials/PytorchCaffe2SuperResolution.ipynb)
 * [Transferring SqueezeNet from PyTorch to Caffe2 and to Android app](tutorials/PytorchCaffe2MobileSqueezeNet.ipynb)
 * [Serving PyTorch Models on AWS Lambda with Caffe2 & ONNX](https://machinelearnings.co/serving-pytorch-models-on-aws-lambda-with-caffe2-onnx-7b096806cfac)