readme: update link to docs.
readme: update link to docs.

davetcoleman/moveit,davetcoleman/moveit,davetcoleman/moveit,v4hn/moveit,davetcoleman/moveit,ros-planning/moveit,ros-planning/moveit,v4hn/moveit,v4hn/moveit,ros-planning/moveit,ros-planning/moveit,v4hn/moveit,ros-planning/moveit