PyPi install when Adafruit Blinka only required for example

[kattni]

We need to document that Adafruit Blinka will likely be needed to use with the example, because it is not a requirement for the library, as the UART object is passed in.

Related to #979

Documentation needed for the following libraries:

• GPS
• Pixie
• FancyLED?
• Waveform

[dhalbert]

@kattni is this still relevant? (Just making a pass through some issues.)

[kattni]

@dhalbert I don't think so. I think we ended up adding Blinka for everything anyway. If not, we'll sort it on the library end.