Update docker documentation with better advice on running containers long-term

The docker documentation should be revised with some better information for running the containers long-term. In particular, better direction on how to run the containers so psconfig files do not need to be re-configured each time the container is restarted/recreated or get wiped out with other temp files. Topics to cover:

• Better highlight that the current command without any shared volumes will result in loss of the psconfig changes on restart. Also note that by default docker mounts new files added to the container to a directory in /tmp which may get overwritten if cronjob or similar on system cleans that out periodically.
• Provide basic instructions for setting up a psconfig directory (maybe a pointer to a shell script or just give the commands directly)
• Provide a docker command with the option to create the shared volume. Also may want to provide the option to restart on failure.
• May want to consider providing a docker-compose file in addition to the raw docker command since that is easier in the long-run (but may be confusing to people just getting started with Docker).