added documentation and improved cmake exporting #52

Job	Run time
build_ros2 / build_focal_foxy	4m 48s
build_ros2 / build_jammy_humble	4m 47s
build_ros2 / build_jammy_iron	4m 42s
build_ros2 / build_jammy_rolling	3m 59s
	18m 16s

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