common: Fingerprint comment

common/byteslice.go

@@ -4,6 +4,9 @@ import (
 	"bytes"
 )
 
+// Fingerprint returns the first 6 bytes of a byte slice.
+// If the slice is less than 6 bytes, the fingerprint
+// contains trailing zeroes.
 func Fingerprint(slice []byte) []byte {
 	fingerprint := make([]byte, 6)
 	copy(fingerprint, slice)