Need a new tutorial for running VRX 2.0 on Docker

[M1chaelM]

We used to offer support for users who want to run VRX using Docker. Our old tutorials for this are out of date. We need a new tutorial that makes use of the dockwater repository. We may need to add rocker as a dependency to make the instructions more portable.

[M1chaelM]

Note: this needs to happen before #660

[M1chaelM]

Steps:

• Create Docker install instructions using dockwater repository.
• Separate "Preparing your system" and "preparing docker image" tutorials and add both to the getting started sequence.
• Update tutorials table of contents.

Preparing Your System:

• Check prerequisites.
• Decide host or Docker install.
• If Docker, go to Docker install tutorial.
• Else, install Gazebo, Humble, and prereq debs.

[M1chaelM]

The getting started sequence has now been updated to include this option: https://github.com/osrf/vrx/wiki/getting_started_tutorial

[M1chaelM]

@crvogt Can you please review the Getting Started sequence using Docker?