GUI support for docker. (#379)

Summary:
Thanks for the great repo! I very much like the easy set up via docker. However, one of the first things I did, was to figure out a way to display stuff like images or plots, without having to save them as images. I thought this might be interestering to others as well.

Kind regards.
Pull Request resolved: facebookresearch/detectron2#379

Differential Revision: D18673252

Pulled By: ppwwyyxx

fbshipit-source-id: 4934fae9be0fe778bd1425340a15320ec3fa9bd2

Dockerfile

@@ -2,6 +2,11 @@ FROM nvidia/cuda:10.1-cudnn7-devel
 # To use this Dockerfile:
 # 1. `nvidia-docker build -t detectron2:v0 .`
 # 2. `nvidia-docker run -it --name detectron2 detectron2:v0`
+# 
+# To enable GUI support (Linux):
+# 1. Grant the container temporary access to your x server (will be reverted at reboot of your host): 
+#    `xhost +local:`docker inspect --format='{{ .Config.Hostname }}' detectron2``
+# 2. `nvidia-docker run -it --name detectron2 --env="DISPLAY" --volume="/tmp/.X11-unix:/tmp/.X11-unix:rw" detectron2:v0`
 
 
 ENV DEBIAN_FRONTEND noninteractive