clarify exponential backoff behaviour

internal/pkg/core/backoff/exponential.go

@@ -45,7 +45,10 @@ func (b *ExpBackoff) NextWait() time.Duration {
 	return nextWait
 }
 
-// Wait block until either the timer is completed or channel is done.
+// Wait blocks until either the exponential backoff timer is completed or the
+// done channel is closed.
+// Wait returns true until done is closed. When done is closed, wait returns
+// immediately, therefore callers should always check the return value.
 func (b *ExpBackoff) Wait() bool {
 	b.duration = b.NextWait()