add subversion/wget to docker, add readme (dmlc#1279)

tools/batch/docker/Dockerfile

@@ -4,6 +4,8 @@ FROM nvidia/cuda:10.2-cudnn7-devel-ubuntu18.04
           build-essential \
           locales \
           cmake \
+          wget \
+          subversion \
           git \
           curl \
           vim \

tools/batch/docker/README.md

@@ -0,0 +1,22 @@
+# Updating the Docker for AWS Batch.
+
+Our current batch job dockers are in 747303060528.dkr.ecr.us-east-1.amazonaws.com/gluon-nlp-1. To
+update the docker:
+- update the Dockerfile
+- Make sure docker and docker-compose, as well as the docker python package are installed.
+- Export the AWS account credentials as environment variables
+- CD to the same folder as the Dockerfile and execute the following:
+
+```
+# this executes a command that logs into ECR.
+$(aws ecr get-login --no-include-email --region us-east-1)
+
+# builds the Dockerfile as gluon-nlp-1 docker.
+docker build -t gluon-nlp-1 .
+
+# tags the recent build as gluon-nlp-1:latest, which AWS batch pulls from.
+docker tag gluon-nlp-1:latest 747303060528.dkr.ecr.us-east-1.amazonaws.com/gluon-nlp-1:latest
+
+# pushes the change
+docker push 747303060528.dkr.ecr.us-east-1.amazonaws.com/gluon-nlp-1:latest
+```