chore: add some annotations (#1544)

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

render/protobuf.go

@@ -10,12 +10,14 @@ import (
 	"github.com/golang/protobuf/proto"
 )
 
+// ProtoBuf contains the given interface object.
 type ProtoBuf struct {
 	Data interface{}
 }
 
 var protobufContentType = []string{"application/x-protobuf"}
 
+// Render (ProtoBuf) marshals the given interface object and writes data with custom ContentType.
 func (r ProtoBuf) Render(w http.ResponseWriter) error {
 	r.WriteContentType(w)
 
@@ -28,6 +30,7 @@ func (r ProtoBuf) Render(w http.ResponseWriter) error {
 	return nil
 }
 
+// WriteContentType (ProtoBuf) writes ProtoBuf ContentType.
 func (r ProtoBuf) WriteContentType(w http.ResponseWriter) {
 	writeContentType(w, protobufContentType)
 }