Added arduino libs

libraries/PID/README.txt

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+***************************************************************
+* Arduino PID Library - Version 1.2.0
+* by Brett Beauregard <br3ttb@gmail.com> brettbeauregard.com
+*
+* This Library is licensed under the MIT License
+***************************************************************
+
+ - For an ultra-detailed explanation of why the code is the way it is, please visit: 
+   http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/
+
+ - For function documentation see:  http://playground.arduino.cc/Code/PIDLibrary