[fenix] Add Google Play badge to Readme (mozilla-mobile/fenix#14829)

fenix/README.md

@@ -5,6 +5,8 @@
 
 Fenix (internal codename) is the all-new Firefox for Android browser, based on [GeckoView](https://mozilla.github.io/geckoview/) and [Mozilla Android Components](https://mozac.org/).
 
+<a href="https://play.google.com/store/apps/details?id=org.mozilla.firefox" target="_blank"><img src="https://play.google.com/intl/en_us/badges/images/generic/en-play-badge.png" alt="Get it on Google Play" height="90"/></a>
+
 ** 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! **
 
 ## Getting Involved