Adding comment about sample rate

src/main.rs

@@ -56,6 +56,7 @@ use heapless::{consts::*, String};
 
 // The number of ticks in the ADC sampling timer. The timer runs at 100MHz, so the step size is
 // equal to 10ns per tick.
+// Currently, the sample rate is equal to: Fsample = 100/256 MHz = 390.625 KHz
 const ADC_SAMPLE_TICKS: u32 = 256;
 
 // The desired ADC sample processing buffer size.