clarify PR comment docs (#7888)

Author: cathteng

src/docs/product/integrations/source-code-mgmt/github/index.mdx

@@ -224,6 +224,8 @@ If a recently merged pull request is suspected of causing an issue, Sentry will
 
 ![Sentry comment on suspect pull request in GitHub](sentry-github-pr-comment.png)
 
+Sentry will only comment on pull requests less than two weeks old that are associated with suspect commits. The comment will continuously be updated with up to five issues the pull request is suspected to have caused.
+
 This feature will be automatically enabled for you once your GitHub integration has been set up. To disable it, go to **Settings > Integrations > GitHub** and toggle it off.
 
 ![How to disable Sentry comments on GitHub pull requests](github-org-settings.png)