Update README.md

README.md

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 # simple-pid
 
-A simple and easy to use PID controller.
+A simple and easy to use PID controller in Python. If you want a PID controller without external dependencies that just works, this is for you! The PID was designed to be robust with help from [Brett Beauregards guide](http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-introduction/).
+
+Usage is very simple:
+
+```python
+from simple_pid import PID
+pid = PID(1, 0.1, 0.05, setpoint=1)
+
+# assume we have a system we want to control in controlled_system
+v = controlled_system.update(0)
+
+while True:
+    # compute new ouput from the PID according to the systems current value
+    control = pid(v)
+
+    # feed the PID output to the system and get its current value
+    v = controlled_system.update(control)
+```
+
+Complete API documentation can be found [here]().
+
+## Installation