constructor of sensor class is implemented

doc/3_sensor_models/3_3_sensors.md

@@ -1,2 +1,25 @@
 ## 3.3 Sensors
-In this section, Sensors class is implemented for managing and processing data of each sensor models. This class can initialize, update and draw the data of each sensor models.  
+In this section, Sensors class is implemented for managing and processing data of each sensor models. This class can initialize, update and draw the data of each sensor models.  
+
+## 3.3.1 Constructor
+An object of [LiDAR class](/doc/3_sensor_models/3_2_lidar.md) is given to a constructor of this class as an argument. The argument is None as default and is stored as a member variable.  
+```python
+"""
+sensors.py
+
+Author: Shisato Yano
+"""
+
+class Sensors:
+    """
+    Each sensors logic class
+    """
+
+    def __init__(self, lidar=None):
+        """
+        Constructor
+        lidar: lidar object
+        """
+
+        self.lidar = lidar
+```