use rtabmap with recorded bag code example

Example: make rtabmap from recorded bag

$ roscore
$ rosparam set use_sim_time true
$ roslaunch rtabmap_ros rtabmap.launch rtabmap_args:="--delete_db_on_start" rgb_topic:=/kinect2/qhd/image_color_rect depth_topic:=/kinect2/qhd/image_depth_rect camera_info_topic:=/kinect2/qhd/camera_info
$ rosbag play --clock kinect2.bag