add a Get/Put example

covout

+mode: set
+github.com/libp2p/go-buffer-pool/pool.go:51.48,52.17 1 1
+github.com/libp2p/go-buffer-pool/pool.go:55.2,56.43 2 1
+github.com/libp2p/go-buffer-pool/pool.go:59.2,59.38 1 1
+github.com/libp2p/go-buffer-pool/pool.go:52.17,54.3 1 1
+github.com/libp2p/go-buffer-pool/pool.go:56.43,58.3 1 1
+github.com/libp2p/go-buffer-pool/pool.go:63.38,65.26 2 1
+github.com/libp2p/go-buffer-pool/pool.go:68.2,68.43 1 1
+github.com/libp2p/go-buffer-pool/pool.go:71.2,72.23 2 1
+github.com/libp2p/go-buffer-pool/pool.go:65.26,66.16 1 0
+github.com/libp2p/go-buffer-pool/pool.go:68.43,70.3 1 1
+github.com/libp2p/go-buffer-pool/pool.go:77.32,79.2 1 1
+github.com/libp2p/go-buffer-pool/pool.go:82.24,84.2 1 1
+github.com/libp2p/go-buffer-pool/pool.go:87.36,89.2 1 1
+github.com/libp2p/go-buffer-pool/pool.go:92.38,94.32 2 1
+github.com/libp2p/go-buffer-pool/pool.go:97.2,97.17 1 1
+github.com/libp2p/go-buffer-pool/pool.go:94.32,96.3 1 1

pool_test.go

@@ -144,3 +144,13 @@ func BenchmarkPoolOverlflow(b *testing.B) {
 		}
 	})
 }
+
+func ExampleGet() {
+	buf := Get(100)
+	fmt.Println("length", len(buf))
+	fmt.Println("capacity", cap(buf))
+	Put(buf)
+	// Output:
+	// length 100
+	// capacity 128
+}