time: add more docs on Sleep
Merge the comment from runtime/time.goc ("at least")
and also note that negative is okay and won't crash.
I see people going out of their way to avoid passing
a negative value to Sleep.
R=golang-dev, adg, r, alex.brainman
CC=golang-dev
https://golang.org/cl/13271045
diff --git a/src/pkg/time/sleep.go b/src/pkg/time/sleep.go
index 591fa27..4f55beb 100644
--- a/src/pkg/time/sleep.go
+++ b/src/pkg/time/sleep.go
@@ -4,7 +4,8 @@
package time
-// Sleep pauses the current goroutine for the duration d.
+// Sleep pauses the current goroutine for at least the duration d.
+// A negative or zero duration causes Sleep to return immediately.
func Sleep(d Duration)
func nano() int64 {
