update comment in :joint-dof definition #144

Job	Run time
osx	4m 4s
doc	3m 43s
linux (ubuntu:trusty)	3m 53s
catkin	5m 10s
linux (ubuntu:xenial)	5m 16s
linux (ubuntu:bionic)	5m 16s
linux (ubuntu:bionic, PQP)	5m 20s
linux (ubuntu:bionic, BULLET)	5m 16s
linux (ubuntu:focal)	5m 37s
linux (debian:stretch)	5m 15s
linux (osrf/ubuntu_armhf:trusty)	31m 15s
linux (osrf/ubuntu_armhf:xenial)	32m 53s
linux (osrf/ubuntu_arm64:xenial)	34m 16s
linux (arm64v8/ubuntu:bionic)	20m 13s
linux (arm64v8/ubuntu:focal)	24m 13s
linux (osrf/debian_arm64:stretch)	34m 46s
	3h 46m 26s

Provide feedback