Merge pull request #144 from SimonEnsemble/master

Update README.txt

README.txt

@@ -8,4 +8,4 @@
  - 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
+ - For function documentation see:  http://playground.arduino.cc/Code/PIDLibrary (Click "Libraries" on the left panel. The link to the documentation is listed as "PIDLibrary - Provides basic feedback control".)