update README

ArmNavigation/two_joint_arm_to_point_control/two_joint_arm_to_point_control.py

@@ -4,6 +4,10 @@ Left-click the plot to set the goal position of the end effector
 
 Author: Daniel Ingram (daniel-s-ingram)
         Atsushi Sakai (@Atsushi_twi)
+
+Ref: P. I. Corke, "Robotics, Vision & Control", Springer 2017, ISBN 978-3-319-54413-7 p102
+- [Robotics, Vision and Control \| SpringerLink](https://link.springer.com/book/10.1007/978-3-642-20144-8)
+
 """
 
 import matplotlib.pyplot as plt

README.md

@@ -6,9 +6,6 @@
 
 Python codes for robotics algorithm.
 
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 # Table of Contents
    * [What is this?](#what-is-this)
    * [Requirements](#requirements)
@@ -84,11 +81,12 @@ This is a Python code collection of robotics algorithms, especially for autonomo
 
 Features:
 
-1. Widely used and practical algorithms are selected.
+1. Easy to read for understanding each algorithm's basic idea.
 
-2. Minimum dependency.
+2. Widely used and practical algorithms are selected.
+
+3. Minimum dependency.
 
-3. Easy to read for understanding each algorithm's basic idea.
 
 # Requirements
 
@@ -738,8 +736,16 @@ Ref:
 
 Two joint arm to a point control simulation. 
 
+This is a interactive simulation.
+
+You can set the goal position of the end effector with left-click on the ploting area. 
+
 ![3](https://github.com/AtsushiSakai/PythonRobotics/raw/master/ArmNavigation/two_joint_arm_to_point_control/animation.gif)
 
+Ref:
+
+- [P. I. Corke, "Robotics, Vision and Control" \| SpringerLink p102](https://link.springer.com/book/10.1007/978-3-642-20144-8)
+
 
 # License 
 
@@ -777,7 +783,3 @@ PayPal donation is also welcome.
 
 - [Alexis Paques](https://github.com/AlexisTM)
 
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