README instructions for demo with docker (#206)

demo/README.md

@@ -2,6 +2,9 @@
 
 This folder contains a simple webcam demo that illustrates how you can use `maskrcnn_benchmark` for inference.
 
+
+### With your preferred environment
+
 You can start it by running it from this folder, using one of the following commands:
 ```bash
 # by default, it runs on the GPU
@@ -14,3 +17,29 @@ python webcam.py --config-file ../configs/caffe2/e2e_mask_rcnn_R_101_FPN_1x_caff
 # in order to see the probability heatmaps, pass --show-mask-heatmaps
 python webcam.py --min-image-size 300 --show-mask-heatmaps MODEL.DEVICE cpu
 ```
+
+### With Docker
+
+Build the image with the tag `maskrcnn-benchmark` (check [INSTALL.md](../INSTALL.md) for instructions)
+
+Adjust permissions of the X server host (be careful with this step, refer to 
+[here](http://wiki.ros.org/docker/Tutorials/GUI) for alternatives)
+
+```bash
+xhost +
+``` 
+
+Then run a container with the demo:
+ 
+```
+docker run --rm -it \
+    -e DISPLAY=${DISPLAY} \
+    --privileged \
+    -v /tmp/.X11-unix:/tmp/.X11-unix \
+    --device=/dev/video0:/dev/video0 \
+    --ipc=host maskrcnn-benchmark \
+    python demo/webcam.py --min-image-size 300
+```
+
+**DISCLAIMER:** *This was tested for an Ubuntu 16.04 machine, 
+the volume mapping may vary depending on your platform*