Provide reference examples for custom ROS recipes

[robwoolley]

New developers have to contend with learning both ROS/Ament and OpenEmbedded/Bitbake at the same time.

It would be beneficial to provide some reference examples of how to create recipes for custom msgs, interface, services, etc using meta-ros.

See this issue for a real-life example: https://github.com/ros/meta-ros/issues/978

[Ryanf55]

Work is started here: https://github.com/Ryanf55/poky/wiki