add Limiter.Wait() example

example_test.go

@@ -0,0 +1,29 @@
+package rate_test
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/linkdata/rate"
+)
+
+func ExampleLimiter_Wait() {
+	var limiter rate.Limiter
+	var now time.Time
+	maxrate := int32(1000)
+
+	// This doesn't wait at all since we haven't waited for anything yet.
+	now = time.Now()
+	limiter.Wait(&maxrate)
+	zeroElapsed := time.Since(now)
+
+	// This waits at least 1ms.
+	maxrate = 1000
+	now = time.Now()
+	limiter.Wait(&maxrate)
+	someElapsed := time.Since(now)
+
+	fmt.Println(zeroElapsed < someElapsed, someElapsed >= time.Millisecond)
+	// Output:
+	// true true
+}