Create instructions to run a node on Docker

[whoabuddy]

From two conversations that started on Discord, there is some interest for instructions on how to run a node using Docker.

@wileyj provided the basic instructions below to start:

essentially, you'll need to create a local config similar to https://docs.blockstack.org/mining , then run the container with any additional env vars you want, bind-mount the config you've created, and set the docker container command to something like stacks-node start --config=<your bind-mounted config>

the container to use is blockstack/stacks-blockchain:latest from https://hub.docker.com/repository/docker/blockstack/stacks-blockchain