Add ros2_control_node to documentation

[christophfroehlich]

I realized that we don't mention the ros2_control_node not even once in the docs. Should we?

Originally posted by @christophfroehlich in #1820 (review)

[fmauch]

This is not entirely true, as we mention it e.g. here but it could definitely placed more visible.

Should we add and explain a minimal launch file with

• description
• controller config file
• robot state publisher
• ros2_control_node
• controller spawner
• RViz

This almost boils down to the launch setup from example1, so we could just try to explain that a bit more in detail and link to that explanation from the getting_started page?

[christophfroehlich]

ah, you are right. In the demos we don't explain what this node is for. I would maybe extend the get started section a bit, and describe parameters like introduced with #1820? And then link to example_1.

[saikishor]

ah, you are right. In the demos we don't explain what this node is for. I would maybe extend the get started section a bit, and describe parameters like introduced with #1820? And then link to example_1.

Yes! some overview of the parameters and what is is used for and a link to an example should do