Add product image

Author: PaulZC

README.md

@@ -1,7 +1,7 @@
 SparkFun GNSSDO
 ========================================
 
-[![SparkFun GNSSDO]()]()
+[![SparkFun GNSSDO](https://cdn.sparkfun.com/r/600-600/assets/parts/2/7/2/0/7/26289-GNSS-Disciplined-Oscillator-Front-Lit.jpg)](https://www.sparkfun.com/products/26289)
 
 [*SparkFun GNSSDO (GPS-26289)*](https://www.sparkfun.com/products/26289)