Update README.md

Author: ttt43ttt

README.md

@@ -2,7 +2,24 @@
 A simple command-line HTTP server
 
 ## Usage:
-```
+```sh
 cd path/to/web-folder/
 http-server start
 ```
+
+## Help Doc:
+```sh
+% http-server start --help
+Start the HTTP server
+
+Usage:
+  http-server start [flags]
+
+Flags:
+  -d, --directory string   Path of the web folder
+  -f, --file string        Path of a file (for sharing a single file)
+  -h, --help               help for start
+  -p, --port int           Port number (default 8080)
+      --qrcode             Show QR code of server URL
+      --upload             Allow uploading files via path /upload
+```