Update README.md (#8588) (#8591)

(cherry picked from commit 4f710ef)

Co-authored-by: Amy Blais <[email protected]>

Author: mattermost-build

README.md

@@ -1,7 +1,7 @@
 # Mattermost Mobile v2
 
 - **Minimum Server versions:** Current ESR version (9.11.0+)
-- **Supported iOS versions:** 13.4+
+- **Supported iOS versions:** 15.1+
 - **Supported Android versions:** 7.0+
 
 Mattermost is an open source Slack-alternative used by thousands of companies around the world in 21 languages. Learn more at [https://mattermost.com](https://mattermost.com).