Provide more command line help

In this change I propose an alternative help message for command line users which lists all available commands and the associated parameters. This makes activator commands and sub commands more discoverable.
"Open an existing project in UI mode if already in a project directory, or open a project-creation UI if no project is found"
? You can probably improve on that.

Rather than saying recommended, why don't we just list UI mode first, and then command line mode right after. I don't think we care that much which mode people pick but if they have no idea maybe UI is a better starting point.