doc: update guide.

Author: cangzhang

README.md

@@ -1,5 +1,12 @@
 # Coding plugin for VS Code.
 
+## How to use
+
+1. Install the plugin
+1. Open a repo host by `coding.net`
+1. Click on `Log in` button
+1. You will be redirected back to the editor, free to try & open an issue
+
 ## Development
 
 - Open this example in VS Code 1.47+