Fix comment (#45)

Fixes #39

Author: sethvargo

internal/fasttime/fasttime.go

@@ -11,8 +11,9 @@ import (
 //go:linkname now time.now
 func now() (sec int64, nsec int32, mono int64)
 
-// Now returns a monotonic clock value. The actual value will differ across
-// systems, but that's okay because we generally only care about the deltas.
+// Now returns a monotonic and wall clock value. The actual value will differ
+// across systems, but that's okay because we generally only care about the
+// deltas.
 func Now() uint64 {
 	sec, nsec, _ := now()
 	return uint64(sec)*1e9 + uint64(nsec)