fix issue #72: add example with context

README.md

@@ -33,6 +33,27 @@ $ retry --infinite -timeout 10m -backoff=lin:500ms -- /bin/sh -c 'echo "trying..
 
 See more details [here](cmd/retry).
 
+### Use context for cancellation
+
+This example shows how to use context and retry together.
+
+```go
+communication := make(chan error)
+
+go service.Listen(communication)
+
+action := func(uint) error {
+	communication <- nil   // ping
+	return <-communication // pong
+}
+ctx := retry.WithContext(context.Background(), retry.WithTimeout(time.Second))
+if err := retry.Retry(ctx.Done(), action, strategy.Delay(time.Millisecond)); err != nil {
+	// the service does not respond within one second
+}
+```
+
+See more details [here](https://godoc.org/github.com/kamilsk/retry#example-package--RetryWithContext).
+
 ### Interrupt execution
 
 ```go

example_retry_with_context_test.go

@@ -0,0 +1,44 @@
+// +build go1.7
+
+package retry_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/kamilsk/retry"
+	"github.com/kamilsk/retry/strategy"
+)
+
+// This example shows how to use context and retry together.
+func Example_retryWithContext() {
+	const expected = 3
+
+	attempts := 3
+	communication := make(chan error)
+	go func() {
+		for {
+			<-communication
+			if attempts == 0 {
+				close(communication)
+				return
+			}
+			attempts--
+			communication <- errors.New("service unavailable")
+		}
+	}()
+
+	action := func(uint) error {
+		communication <- nil   // ping
+		return <-communication // pong
+	}
+	ctx := retry.WithContext(context.Background(), retry.WithTimeout(time.Second))
+	if err := retry.Retry(ctx.Done(), action, strategy.Delay(time.Millisecond)); err != nil {
+		panic(err)
+	}
+
+	fmt.Printf("attempts: %d, expected: %d \n", expected-attempts, expected)
+	// Output: attempts: 3, expected: 3
+}