Add link to forum thread about RNGA code & results

teensy3/kinetis.h

@@ -2795,6 +2795,8 @@ typedef struct {
 
 // Random Number Generator Accelerator (RNGA)
 
+// For info about using RNGA and the quality of its results:
+// https://forum.pjrc.com/threads/48745-Teensy-3-6-Random-Number-Generator
 #define RNG_CR			(*(volatile uint32_t *)0x40029000) // RNGA Control Register
 #define RNG_SR			(*(volatile uint32_t *)0x40029004) // RNGA Status Register
 #define RNG_ER			(*(volatile uint32_t *)0x40029008) // RNGA Entropy Register