docs: tips for set port

vue.config.js

@@ -7,6 +7,9 @@ function resolve(dir) {
 }
 
 const name = defaultSettings.title || 'vue Element Admin' // page title
+// If your port is set to 80,
+// use administrator privileges to execute the command line.
+// For example, Mac: sudo npm run
 const port = 9527 // dev port
 
 // All configuration item explanations can be find in https://cli.vuejs.org/config/