Update README.md

- add library tiering

Author: alanjcharles

README.md

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 ![](https://github.com/segmentio/analytics-swift/actions/workflows/swift.yml/badge.svg)
 ![](https://img.shields.io/github/license/segmentio/analytics-swift)
 
+### 🎉 Flagship 🎉
+This library is one of Segment’s most popular Flagship libraries. It is actively maintained by Segment, benefitting from new feature releases and ongoing support.
+
 The hassle-free way to add Segment analytics to your Swift app (iOS/tvOS/visionOS/watchOS/macOS/Linux/iPadOS). Analytics helps you measure your users, product, and business. It unlocks insights into your app's funnel, core business metrics, and whether you have product-market fit.
 
 ## How to get started