feat: update cropbox filter README

Signed-off-by: yoshiri <yoshiyoshidetteiu@gmail.com>

Author: YoshiRi

sensing/pointcloud_preprocessor/docs/crop-box-filter.md

@@ -4,9 +4,15 @@
 
 The `crop_box_filter` is a node that removes points with in a given box region. This filter is used to remove the points that hit the vehicle itself.
 
+There are two nodes belongs to this package.
+
+- `crop_box_filter_node`: This node is a ROS2 node that subscribes to a point cloud topic and publishes the filtered point cloud topic.
+- `crop_boxes_filter_node`: This node has same functionality as `crop_box_filter_node`, but it can handle multiple crop boxes.
+
 ## Inner-workings / Algorithms
 
-`pcl::CropBox` is used, which filters all points inside a given box.
+Crop box filter is a simple filter that removes points inside a given box.
+Remember cropbox coordinate is defined in the `input_frame` frame.
 
 ## Inputs / Outputs
 
@@ -20,6 +26,8 @@ This implementation inherit `pointcloud_preprocessor::Filter` class, please refe
 
 ### Core Parameters
 
+For `crop_box_filter_node` and `crop_boxes_filter_node`, the following parameters are used to describe each cropbox.
+
 | Name    | Type   | Default Value | Description                               |
 | ------- | ------ | ------------- | ----------------------------------------- |
 | `min_x` | double | -1.0          | x-coordinate minimum value for crop range |
@@ -29,6 +37,34 @@ This implementation inherit `pointcloud_preprocessor::Filter` class, please refe
 | `min_z` | double | -1.0          | z-coordinate minimum value for crop range |
 | `max_z` | double | 1.0           | z-coordinate maximum value for crop range |
 
+For multiple crop boxes in `crop_boxes_filter_node`, the following parameters are used to describe each cropbox.
+
+| Name               | Type     | Default Value | Description                                                           |
+| ------------------ | -------- | ------------- | --------------------------------------------------------------------- |
+| `crop_boxes_names` | string[] | []            | Names of crop boxes                                                   |
+| `crop_boxes`       | map      | {}            | Map of crop boxes. Each crop box is described by the above parameters |
+
+Example of `crop_boxes` parameter is:
+
+```yaml
+crop_boxes_names: ["right", "left"]
+crop_boxes:
+  right:
+    min_longitudinal_offset: 4.8
+    max_longitudinal_offset: 5.3
+    min_lateral_offset: -1.3
+    max_lateral_offset: -1.05
+    min_height_offset: 1.85
+    max_height_offset: 2.59
+  left:
+    min_longitudinal_offset: 4.83
+    max_longitudinal_offset: 6.0
+    min_lateral_offset: 0.95
+    max_lateral_offset: 1.28
+    min_height_offset: 1.95
+    max_height_offset: 2.6
+```
+
 ## Assumptions / Known limits
 
 ## (Optional) Error detection and handling