update SERVICE_TOKEN description

Author: wj-Mcat

README.md

@@ -39,8 +39,8 @@ Wechaty is a RPA SDK for Wechat **Individual** Account that can help you create
     ```sh
     # examples/ding-dong-bot.py : func-> main()
     # it must be donut token
-    export WECHATY_PUPPET=wechaty-puppet-hostie
-    export WECHATY_PUPPET_HOSTIE_TOKEN=your_token_at_here
+    export WECHATY_PUPPET=wechaty-puppet-service
+    export WECHATY_PUPPET_SERVICE_TOKEN=your_token_at_here
     ```
 
 4. Run the bot