update docs with link unfurl

Author: yasunariw

README.md

@@ -40,6 +40,14 @@ Run the `_build/default/src/monorobot.exe` binary. The following commands are su
         - **Incoming Webhooks:** To use [incoming webhooks](https://api.slack.com/messaging/webhooks), enable them in your app dashboard and create one for each channel you want to notify. Store them in the `slack_hooks` field of your secrets file. If you decide to notify additional channels later, you will need to update the secrets file with the new webhooks and restart the server.
 
 
+### Link Unfurling
+
+You can configure Monorobot to [unfurl GitHub links](https://api.slack.com/reference/messaging/link-unfurling) in Slack messages. Currently, commit links are supported.
+
+1. Give your app `links:read` and `links:write` [permissions](https://api.slack.com/apps).
+1. Configure your app to [support the Events API](https://api.slack.com/events-api#prepare). During the [url verification handshake](https://api.slack.com/events-api#the-events-api__subscribing-to-event-types__events-api-request-urls__request-url-configuration--verification__url-verification-handshake), you should tell Slack to direct event notifications to `<server_domain>/slack/events`. Ensure the server is running before triggering the handshake.
+1. [Register the GitHub domains](https://api.slack.com/reference/messaging/link-unfurling#configuring_domains) you want to support.
+
 ### Documentation
 
 The bot expects two configuration files to be present.