chore: add some annotations (#1544)

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

render/render.go

@@ -6,8 +6,11 @@ package render
 
 import "net/http"
 
+// Render interface is to be implemented by JSON, XML, HTML, YAML and so on.
 type Render interface {
+	// Render writes data with custom ContentType.
 	Render(http.ResponseWriter) error
+	// WriteContentType writes custom ContentType.
 	WriteContentType(w http.ResponseWriter)
 }