use full name of pixelbuf library

Author: FoamyGuy

README.rst

@@ -38,7 +38,7 @@ Dependencies
 This driver depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
-* `adafruit_pixelbuf library <https://github.com/adafruit/Adafruit_CircuitPython_Pixelbuf>`_
+* `Adafruit CircuitPython Pixelbuf library <https://github.com/adafruit/Adafruit_CircuitPython_Pixelbuf>`_
 
 Please ensure all dependencies are available on the CircuitPython filesystem.
 This is easily achieved by downloading