[fenix] Closes https://github.com/mozilla-mobile/fenix/issues/4775 - Update README with Severity Triage process (https://github.com/mozilla-mobile/fenix/pull/6311)

README.md

@@ -5,6 +5,8 @@
 
 Firefox Preview (internal code name: "Fenix") is an all-new browser for Android, based on [GeckoView](https://mozilla.github.io/geckoview/) and [Mozilla Android Components](https://mozac.org/).
 
+** Note: The team is currently experiencing heavy triage and review load, so when triaging issues, we will mainly be looking to identify [S1 (high severity)](https://github.com/mozilla-mobile/fenix/labels/S1) issues. See our triage process [here](https://github.com/mozilla-mobile/fenix/wiki/Triage-Process). Please be patient if you don't hear back from us immediately on your issue! **
+
 ## I want to open a Pull Request!
 
 We encourage you to participate in this open source project. We love Pull Requests, Bug Reports, ideas, (security) code reviews or any other kind of positive contribution.