Document that h2o k8s images doesn't apply security settings by default

[mn-mikke]

Please add note to H2O documentation and to dockerhub that official k8s images doesn't apply any security settings and the default user is ROOT.

if user requires a secured interface with h2o running in the image, it's his/her responsibility to change user and execution command to add security parameters before running the image.

Docker images:

• https://hub.docker.com/r/h2oai/h2o-open-source-k8s
• https://hub.docker.com/r/h2oai/h2o-open-source-k8s-minimal

Default command used in docker images:
java -Djava.library.path=/opt/h2oai/h2o-3/xgb_lib_dir -XX:+UseContainerSupport -XX:MaxRAMPercentage=50 -jar /opt/h2oai/h2o-3/h2o.jar

[hannah-tillman]

@mn-mikke I've never edited anything on dockerhub before -- I don't believe I have access at the moment.