docs(lane_change): add description for lane expansion (#6251)

* docs(lane_change): add description for lane expansion

Signed-off-by: Fumiya Watanabe <rej55.g@gmail.com>

* Update planning/behavior_path_lane_change_module/README.md

Co-authored-by: Zulfaqar Azmi <93502286+zulfaqar-azmi-t4@users.noreply.github.com>

* Update planning/behavior_path_lane_change_module/README.md

Co-authored-by: Zulfaqar Azmi <93502286+zulfaqar-azmi-t4@users.noreply.github.com>

---------

Signed-off-by: Fumiya Watanabe <rej55.g@gmail.com>
Co-authored-by: Zulfaqar Azmi <93502286+zulfaqar-azmi-t4@users.noreply.github.com>

Author: rej55

planning/behavior_path_lane_change_module/README.md

@@ -361,6 +361,13 @@ The following parameters are configurable in `lane_change.param.yaml`.
 
 The following parameters are configurable in `behavior_path_planner.param.yaml` and `lane_change.param.yaml`.
 
+#### common
+
+| Name                                       | Unit | Type   | Description                                                                                                                                 | Default value |
+| :----------------------------------------- | ---- | ------ | ------------------------------------------------------------------------------------------------------------------------------------------- | ------------- |
+| `safety_check.lane_expansion.left_offset`  | [m]  | double | Expand the left boundary of the detection area, allowing objects previously outside on the left to be detected and registered as targets.   | 0.0           |
+| `safety_check.lane_expansion.right_offset` | [m]  | double | Expand the right boundary of the detection area, allowing objects previously outside on the right to be detected and registered as targets. | 0.0           |
+
 #### execution
 
 | Name                                                              | Unit    | Type    | Description                                                                                                                                                    | Default value |