additional explanation in the readme

Signed-off-by: Zulfaqar Azmi <[email protected]>

planning/behavior_path_planner/README.md

@@ -38,9 +38,15 @@ WIP
 
 ---
 
-### Manager design
+### Planner Manager design
 
-The role of manager is to launch the appropriate scene module according to the situation. (e.g. if there is parked-vehicle in ego's driving lane, the manager launches the avoidance module.)
+The Planner Manager's responsibilities include:
+
+1. Activating the relevant scene module in response to the specific situation faced by the autonomous vehicle. For example, when a parked vehicle block ego vehicle's driving lane, the manager would engage the avoidance module.
+2. Managing the execution order of when multiple modules are running at the same time. If, for instance, both lane-changing and avoidance modules are operational, the manager decides which should take precedence.
+3. When multiple modules are activated simultaneously and each generates its own path, the manager merges these into a single functional path.
+
+For more in-depth information, refer to [Manager design](https://autowarefoundation.github.io/autoware.universe/main/planning/behavior_path_planner/docs/behavior_path_planner_manager_design/) document.
 
 ## Inputs / Outputs / API
 
@@ -59,6 +65,9 @@ The role of manager is to launch the appropriate scene module according to the s
 | ~/input/lateral_offset        |     △     | `tier4_planning_msgs::msg::LateralOffset`              | lateral offset to trigger side shift                                                                                                                                                                                     |
 | ~/system/operation_mode/state |     ○     | `autoware_adapi_v1_msgs::msg::OperationModeState`      | Allows planning module to know if vehicle is in autonomous mode or can be controlled<sup>[ref](https://github.com/autowarefoundation/autoware.universe/blob/main/system/default_ad_api/document/operation-mode.md)</sup> |
 
+- ○ Mandatory: Planning Module would not work if anyone of this is not present.
+- △ Optional: Some module would not work, but Planning Module can still be operated.
+
 ### Output
 
 | Name                        | Type                                                     | Description                                                                                    |
@@ -70,9 +79,6 @@ The role of manager is to launch the appropriate scene module according to the s
 | ~/input/ready_module        | `tier4_planning_msgs::msg::PathChangeModule`             | (for remote control) modules that are ready to be executed.                                    |
 | ~/input/running_modules     | `tier4_planning_msgs::msg::PathChangeModuleArray`        | (for remote control) current running module.                                                   |
 
-○ Mandatory: Planning Module would not work if anyone of this is not present.
-△ Optional: Some module would not work, but Planning Module can still be operated.
-
 ## General features of behavior path planner
 
 ### Drivable area generation logic