modify README due to specification changes

I cannot use snippet 😢

README.md

@@ -125,13 +125,19 @@ At first, you need to create new app. Please access https://api.slack.com/apps.
 #### Basic Information
 
 1. click `Permissions` on `Add features and functionality`
-2. select `files:write:user` on `Scopes` and click `Save Changes`
+2. select `files:write:user` on `Scopes` and click `Save Changes`. You are able to choose `Bot Token Scopes` or `User Token Scopes`
 
 #### OAuth & Permissions
 
 1. click `Install App to Workspace`
 2. install your app
-3. copy `OAuth Access Token` beginning with `xoxp-`
+3. copy `OAuth Access Token` beginning with `xoxp-` or `Bot User OAuth Access Token` beginning with `xoxb-`
+
+#### Add apps
+
+1. click `Details` on the channel which you want to post
+2. click `Add apps` on `More`
+3. choose your app
 
 ### (Advanced) Environment Variables