Update README.md

README.md

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 # pico_ws2812b
 a library for using WS2812b leds (aka neopixels) with Raspberry Pi Pico
+
+You'll first need to save the ws2812b.py file to your device (for example, open it in Thonny and go file > save as and select MicroPython device. Give it the same name). Once it's there, you can import it into your code. 
+
+You create an object with the parameters number of LEDs, state machine ID and GPIO number in that order. so, to create a strip of 10 leds on state machine 0 and GPIO 0, you use:
+
+```
+pixels = ws2812b.ws2812b(10,0,0)
+```
+
+This object has two methods, show() which sends the data to the strip, and set_pixel which sets the colour values for a particular LED. The parameters are LED number, red, green, blue with the colours taking values between 0 and 255.
+
+A simple example is the following typed into the interpreter:
+
+```
+>>> import ws2812b
+>>> pixels = ws2812b.ws2812b(10,0,0)
+>>> pixels.show()
+>>> pixels.set_pixel(5,10,0,0)
+>>> pixels.show()
+>>> pixels.set_pixel(5,0,10,0)
+>>> pixels.show()
+```
+
+Pull requests are open if you'd like more features!