feat(chore): show up help if no args were passed (#72)

* feat: show up help if no args were passed

closes #71

* chore: update warning message

* chore: minor tweak

Author: jamesgeorge007

bin/docsify

@@ -18,6 +18,7 @@ require("yargonaut")
   .errorsStyle("red.bold");
 
 const yargs = require("yargs")
+  .demandCommand(1, chalk.red("[ERROR] 0 arguments passed. Please specify a command"))
   .usage(chalk.bold(y18n.__("usage") + ": docsify <init|serve> <path>"))
   .command({
     command: "init [path]",