Add deprecation content

Author: krollins-mdb

source/deprecation.txt

@@ -13,4 +13,25 @@ Atlas Device SDKs Deprecation
    :depth: 2
    :class: singlecol
 
+As of September 2024, Atlas Device SDKs are deprecated. Atlas Device SDKs will
+reach end-of-life and be removed on **September 30, 2025**. 
 
+The Atlas Device SDKs are made up of two parts: the on-device database and
+Atlas Device Sync. The on-device database will continue to exist as an open
+source project.
+
+Atlas Device Sync is deprecated. This means that apps built using Sync need to
+move to an alternative solution or remove Sync before September 30, 2025. Refer
+to the :ref:`App Services deprecation page <app-services-deprecation>` for more information.
+
+Device SDKs Community Branches
+------------------------------
+
+The Device SDKs will have community branches that remove Device Sync code from
+their codebases. Learn more in the SDKs' README files:
+
+- `Flutter <https://github.com/realm/realm-dart>`__
+- `Kotlin <https://github.com/realm/realm-kotlin>`__
+- `.NET <https://github.com/realm/realm-dotnet>`__
+- `JavaScript <https://github.com/realm/realm-js>`__
+- `Swift <https://github.com/realm/realm-swift>`__