Docker readme added with basic operation.

Author: sacherjj

DOCKER_README.md

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+# Container for running casper-node-launcher
+
+Scripts that would be in the `/etc/casper` directory with a normal debian install exist with the
+`casper-node-launcher` executable.
+
+It is expected that users will mount two volumes to the inside of the container at:
+`/etc/casper` and `/var/lib/casper`.
+
+It is also expected that `/etc/casper/validator_keys` exists and is populated by keys from `casper-client keygen`.
+
+For minimum node functionality port 35000 needs to be accessible.  For full functionality, ports 7777, 8888, and 9999
+should also be exposed, unless they have been changed in the config.toml.
+
+Initial configuration will consist of calling:
+`/root/pull_casper_node_version.sh <protocol version> <network name>`
+`/root/config_from_example.sh <protocol version>`