Add Additional Vendor for PiOLED Header

[ghost]

The PiOLED header has been unavailable from Adafruit and Amazon for quite some time, however SparkFun has a suitable substitute in stock (https://www.sparkfun.com/products/12792). Could this be added to the wiki as an alternative?

[jaybdub]

Hi wphuhn,

Thanks for pointing this out! This does look like a suitable alternative. I've added it to the bill of materials as an alternate source.

Thanks!
John