Deprecate Dynamic Links (#5649)

Author: morganchen12

firebase-dynamic-links/README.md

@@ -0,0 +1,7 @@
+Firebase Dynamic Links
+======================
+
+> [!IMPORTANT]
+> Firebase Dynamic Links is **deprecated** and should not be used in new projects. The service will shut down on August 25, 2025.
+>
+> Please see our [Dynamic Links Deprecation FAQ documentation](https://firebase.google.com/support/dynamic-links-faq) for more guidance.