Add Warnings documentation

index.js

@@ -59,7 +59,7 @@ const gitHubEvents = () => JSON.parse(fs.readFileSync(eventPath, 'utf8'));
 const commitMessage = () => {
     const event = gitHubEvents();
     if (!event || !event.commits || !event.commits.length > 0) {
-        core.warning('No commit message found in Event:\n' + JSON.stringify(event));
+        core.warning('No commit message found in Event!\n' + JSON.stringify(event));
         return '[[no-commit-message-found!]]';
     }
     return event.commits[event.commits.length - 1].message

readme.md

@@ -117,6 +117,20 @@ Do not forget to add your secret and your custom Slack Block Kit JSON:
 
 Your [Incoming WebHook](https://api.slack.com/messaging/webhooks) URL `slack_web_hook_url` is not valid.
 
+## Warnings
+
+### Could not get slack mention mapping!
+
+Your `slack_mention_mapping_file` path is wrong or content is not JSON.
+
+### No commit message found in Event!
+
+The GitHub Event has no commit which could be displayed. The content of the file should be:
+
+> The path of the file with the complete webhook event payload. For example, /github/workflow/event.json.
+
+More information in the [GitHub Actions Docs](https://docs.github.com/en/free-pro-team@latest/actions/reference/environment-variables#default-environment-variables) under environment variable `GITHUB_EVENT_PATH`.
+
 # License
 
 Licensed under [MIT](./LICENSE).