chore: add some annotations (#1544)

ref: #1075 
because I am not a native English, maybe have a bit problem.

render/msgpack.go

@@ -10,20 +10,24 @@ import (
 	"github.com/ugorji/go/codec"
 )
 
+// MsgPack contains the given interface object.
 type MsgPack struct {
 	Data interface{}
 }
 
 var msgpackContentType = []string{"application/msgpack; charset=utf-8"}
 
+// WriteContentType (MsgPack) writes MsgPack ContentType.
 func (r MsgPack) WriteContentType(w http.ResponseWriter) {
 	writeContentType(w, msgpackContentType)
 }
 
+// Render (MsgPack) encodes the given interface object and writes data with custom ContentType.
 func (r MsgPack) Render(w http.ResponseWriter) error {
 	return WriteMsgPack(w, r.Data)
 }
 
+// WriteMsgPack writes MsgPack ContentType and encodes the given interface object.
 func WriteMsgPack(w http.ResponseWriter, obj interface{}) error {
 	writeContentType(w, msgpackContentType)
 	var mh codec.MsgpackHandle