update --rewrite option description

lib/cli-options.js

@@ -26,7 +26,7 @@ module.exports = {
     },
     {
       name: 'rewrite', alias: 'r', type: String, multiple: true, typeLabel: '[underline]{expression} ...',
-      description: "A list of URL rewrite rules, e.g. '/from -> /to'", group: 'server'
+      description: "A list of URL rewrite rules. For each rule, separate the 'from' and 'to' routes with '->'. Whitespace surrounded the routes is ignored. E.g. '/from -> /to'", group: 'server'
     },
     {
       name: 'spa', alias: 's', type: String, typeLabel: '[underline]{file}',