docs(obstacle_stop_planner): update documentation (#880)

Signed-off-by: satoshi-ota <[email protected]>

planning/obstacle_stop_planner/README.md

@@ -11,13 +11,20 @@
 - Adaptive Cruise Controller (ACC)
   - embeds target velocity in trajectory when there is a dynamic point cloud on the trajectory.
 
-When the stop point that has 0 velocity is inserted, the point is inserted in front of the target point cloud by the distance of `baselink to front` + `stop margin`. The `baselink to front` means the distance between `base_link`(center of rear-wheel axis) and front of the car. `stop margin` is determined by the parameters described below.
+In order to stop with a `stop margin` from the obstacle exists, the stop point (`v=0`) is inserted at a distance of `baselink to front` + `stop margin` from the obstacle. The `baselink to front` means the distance between `base_link`(center of rear-wheel axis) and front of the car.
 
-![insert_stop_velocity](./docs/insert_velocity.drawio.svg)
+If a stop point has already been inserted by other nodes between the obstacle and a position which is `stop margin` meters away from the obstacle, the stop point is inserted at a distance of `baselink to front` + `min behavior stop margin` from the obstacle.
+
+<div align="center">
+  <img src="./docs/insert_velocity1.drawio.svg" width=45%>
+  <img src="./docs/insert_velocity2.drawio.svg" width=45%>
+</div>
 
 When the deceleration section is inserted, the start point of the section is inserted in front of the target point cloud by the distance of `baselink to front` + `slow down forward margin`. the end point of the section is inserted behind the target point cloud by the distance of `slow down backward margin` + `baselink to rear`. The `baselink to rear` means the distance between `base_link` and rear of the car. The velocities of points in the deceleration section are modified to the deceleration velocity. `slow down backward margin` and `slow down forward margin` are determined by the parameters described below.
 
-![insert_stop_velocity](./docs/insert_decel_velocity.drawio.svg)
+<div align="center">
+  <img src="./docs/insert_decel_velocity.drawio.svg" width=45%>
+</div>
 
 ## Input topics