docs(traffic_light_estimator): add README

Signed-off-by: satoshi-ota <satoshi.ota928@gmail.com>

perception/traffic_light_estimator/README.md

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+# traffic_light_estimator
+
+## Purpose
+
+`traffic_light_estimator` is a module that estimates pedestrian traffic signals from HDMap and detected vehicle traffic signals.
+
+## Inputs / Outputs
+
+### Input
+
+| Name                                 | Type                                                     | Description        |
+| ------------------------------------ | -------------------------------------------------------- | ------------------ |
+| `~/input/vector_map`                 | `autoware_auto_mapping_msgs::msg::HADMapBin`             | vector map         |
+| `~/input/route`                      | `autoware_auto_planning_msgs::msg::HADMapRoute`          | route              |
+| `~/input/classified/traffic_signals` | `autoware_auto_perception_msgs::msg::TrafficSignalArray` | classified signals |
+
+### Output
+
+| Name                       | Type                                                     | Description                                               |
+| -------------------------- | -------------------------------------------------------- | --------------------------------------------------------- |
+| `~/output/traffic_signals` | `autoware_auto_perception_msgs::msg::TrafficSignalArray` | output that contains estimated pedestrian traffic signals |
+
+## Parameters
+
+| Name                    | Type   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | Default value |
+| :---------------------- | :----- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :------------ |
+| `use_last_detect_color` | `bool` | If this parameter is `true`, this module estimates pedestrian's traffic signal as RED not only when vehicle's traffic signal is detected as GREEN but also when detection results change GREEN to UNKNOWN. (If detection results change RED or AMBER to UNKNOWN, this module estimates pedestrian's traffic signal as UNKNOWN.) If this parameter is `false`, this module use only latest detection results for estimation. (Only when the detection result is GREEN, this module estimates pedestrian's traffic signal as RED.) | `true`        |
+
+## Inner-workings / Algorithms
+
+```plantuml
+
+start
+:subscribe detected traffic signals;
+:get crosswalk lanelets;
+:extract road lanelets that conflicts crosswalk;
+if (Is there **STRAIGHT-GREEN** road lanelet?) then (yes)
+  :estimate related pedestrian's traffic signal as **RED**;
+else if (Is there both **LEFT-GREEN** and **RIGHT-GREEN** road lanelet?) then (yes)
+  :estimate related pedestrian's traffic signal as **RED**;
+else
+  :estimate related pedestrian's traffic signal as **UNKNOWN**;
+endif
+end
+
+```
+
+If traffic between pedestrians and vehicles is controlled by traffic signals, the crosswalk traffic signal maybe **RED** in order to prevent pedestrian from crossing when the following conditions are satisfied.
+
+### Situation1
+
+- crosswalk conflicts **STRAIGHT** lanelet
+- the lanelet refers **GREEN** traffic signal
+
+<div align="center">
+  <img src="images/straight.drawio.svg" width=80%>
+</div>
+<div align="center">
+  <img src="images/intersection1.svg" width=80%>
+</div>
+
+### Situation2
+
+- crosswalk conflicts different turn direction lanelets (STRAIGHT and LEFT, LEFT and RIGHT, RIGHT and STRAIGHT)
+- the lanelets refer **GREEN** traffic signal
+
+<div align="center">
+  <img src="images/intersection2.svg" width=80%>
+</div>
+
+## Assumptions / Known limits
+
+## Future extensions / Unimplemented parts