feat(cli): support completion rules

via asynchronous promise

Author: jrappen

bin/docsify

@@ -68,6 +68,13 @@ var argv = require('yargs')
     }),
     handler: (argv) => run.serve(argv.path, argv.open, argv.port)
   })
+  .completion('completion', function (current, argv, done) {
+    return new Promise(function (resolve, reject) {
+      setTimeout(function () {
+        resolve(['init', 'serve'])
+      }, 10)
+    })
+  })
   .help()
   .option('help', {
     alias: 'h',