Add support for demo mode in docker. roundup/demo.py Make changes to allow exposed port in docker to be specified separately from the port that demo mode binds to. Also permit bind address specification as well. roundup/scripts/roundup_demo.py: Update required by changes in demo.py. Also move away from positional arguments to prefer flag arguments. Required for passing port and host specification. Flake8 fixes. share/man/man1/roundup-demo.1 Document use of option flags rather than positional params. Other cleanups. doc/installation.txt: Document new docker modes: demo, shell and admin. Update docs: overview section - reorg, added template info for the impatient section - added docker demo mode reference, more docs on top level demo.py use. new section on docker demo mode removed getting roundup section. folded into installing roundup. also prior for the impatient section describes how to download. install via pip in venv recommended supported method document all provided templates. not just minimal and classic. added index references. move sections around, decreased sectin depth, reformatting scripts/Docker/roundup_healthcheck: When running roundup-demo, there is no tracker spec. So default to demo if no tracker=directory args found. Prevent's docker from reporting an unhealthy container when running demo. scripts/Docker/roundup_start: implement demo, shell, admin docker modes.