docs(simple_pure_pursuit): add README (#2)

* add parameter description

Signed-off-by: mitukou1109 <mitukou1109@gmail.com>

* add README

Signed-off-by: mitukou1109 <mitukou1109@gmail.com>

---------

Signed-off-by: mitukou1109 <mitukou1109@gmail.com>

Author: mitukou1109

control/autoware_simple_pure_pursuit/README.md

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+# Simple Pure Pursuit
+
+The `simple_pure_pursuit` node receives a reference trajectory from `motion_velocity_smoother` and calculates the control command using the pure pursuit algorithm.
+
+## Flowchart
+
+![Flowchart](https://www.plantuml.com/plantuml/png/LOuxSWCn28PxJa5fNy5Rn4NkiKCaB3D1Q4T2XMyVeZZEH8q6_iV7TJXrdrN1nPMnsUvIkSFQ0roSFlcTd3QG6vvaO8u1ErD-l9tHxsnuUl0u0-jWG1pU3c3BSWCelSq3KvYTzzJCUzFuQoNBOVqk32tTEMDffF_xCDxbc1yguxvQyPdSbhGuY3-aS2RIj6kp8Zwp6EalS7kfmvcxMDd9Yl86aSLr8i0Bz0pziM21hk6TLRy0)
+
+## Input topics
+
+| Name                 | Type                                        | Description                      |
+| :------------------- | :------------------------------------------ | :------------------------------- |
+| `~/input/odometry`   | `nav_msgs::msg::Odometry`                   | ego odometry                     |
+| `~/input/trajectory` | `autoware_planning_msgs::msg::Trajectory`   | reference trajectory             |
+
+## Output topics
+
+| Name                       | Type                                  | Description     | QoS Durability |
+| :------------------------- | :------------------------------------ | :-------------- | :------------- |
+| `~/output/control_command` | `autoware_control_msgs::msg::Control` | control command | `volatile`     |
+
+## Parameters
+
+{{ json_to_markdown("control/autoware_simple_pure_pursuit/schema/simple_pure_pursuit.schema.json") }}

control/autoware_simple_pure_pursuit/schema/simple_pure_pursuit.schema.json

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+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Parameters for Simple Pure Pursuit Node",
+  "type": "object",
+  "definitions": {
+    "autoware_simple_pure_pursuit": {
+      "type": "object",
+      "properties": {
+        "lookahead_gain": {
+          "type": "number",
+          "description": "Gain for lookahead distance calculation: {lookahead distance} = lookahead_gain * {target velocity} + lookahead_min_distance",
+          "minimum": 0.0
+        },
+        "lookahead_min_distance": {
+          "type": "number",
+          "description": "Minimum lookahead distance [m]",
+          "minimum": 0.0
+        },
+        "speed_proportional_gain": {
+          "type": "number",
+          "description": "Gain for longitudinal acceleration calculation: {longitudinal acceleration} = speed_proportional_gain * ({target velocity} - {current velocity})",
+          "minimum": 0.0
+        },
+        "use_external_target_vel": {
+          "type": "boolean",
+          "description": "Whether to use external target velocity"
+        },
+        "external_target_vel": {
+          "type": "number",
+          "description": "External target velocity [m/s]",
+          "minimum": 0.0
+        }
+      },
+      "required": [
+        "lookahead_gain",
+        "lookahead_min_distance",
+        "speed_proportional_gain",
+        "use_external_target_vel",
+        "external_target_vel"
+      ],
+      "additionalProperties": false
+    }
+  }
+}