Update README

bencode/README

@@ -1 +1,38 @@
 Bencode encoding/decoding sub package. Uses similar API design to Go's json package.
+
+## Install
+
+```sh
+go get github.com/anacrolix/torrent
+```
+
+## Usage
+
+```go
+package demo
+
+import (
+	bencode "github.com/anacrolix/torrent/bencode"
+)
+
+type Message struct {
+	Query    string `json:"q,omitempty" bencode:"q,omitempty"`
+}
+
+var v Message
+
+func main(){
+	// encode
+	data, err := bencode.Marshal(v)
+	if err != nil {
+		log.Fatal(err)
+	}
+	
+	//decode
+	err := bencode.Unmarshal(data, &v)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println(v)
+}
+```