Add Physical Robot info to the new gh-pages documentation

[PaulBouchier]

This issue is to track work items related to introducing linorobot2_hardware and related documentation for a Physical robot to the new gh-pages docs

[PaulBouchier]

Issue moved from PR 197 review into Issue 198, and now into Issue #217

Do something about this issue:

base_controller.md line 2

This section is mis-named - it really isn't centrally about the base controller - though it does have a little summary of what it is. But someone building a physical robot will spend most of their time over in linorobot2_hardware, building and bringing up the physical robot. Suggest:

Base Controller Integration
Then have the summary description of what the base controller is, as below, then a section

Build the Base controller for a physical robot
Follow the tutorial at the URL to linorobot2_hardware github pages to build and test your base controller with its robot hardware.

And maybe retitle "Simulation" as

Configure the Base controller for a simulated robot
The Magnetometer configuration belongs as a subsection under "Base Controller Integration". It is about how to modify the ROS side to accommodate a physical robot base controller that has a magnetometer.

As an observation, this is where you really indicate your preference to keep HW documentation over in linorobot2_hardware. I can work with that. But we need to recognize and guide that this set of pages is only half the story for someone building a physical robot. IOW this set of pages is not stand-alone for someone building a physical robot, it must be read together with the set of pages that will exist in linorobot2_hardware.

[PaulBouchier]

This would be the right place to deal with customizing the URDF, especially for simulation