add guides for PowerSync and Ably (#868)

Author: MongoCaleb

source/sync/device-sync-deprecation.txt

@@ -43,6 +43,9 @@ PowerSync
 PowerSync is a sync engine that keeps backend databases in sync with on-device
 SQLite databases.
 
+For more information on migration, refer to the following:
+
+- `PowerSync Reference Architecture Guide <https://cdn.bfldr.com/2URK6TO/as/v5cmphbnwbhqh89frg5c7xw/MongoDB__PowerSync_Reference_Architecture_Guide>`__
 - `Atlas Device Sync to PowerSync migration guide <https://docs.powersync.com/resources/migration-guides/mongodb-atlas>`__
 
 ObjectBox
@@ -80,7 +83,10 @@ Ably
 Ably is a real-time infrastructure service that uses Pub/Sub APIs in a wide
 variety of SDKs to power live experiences.
 
-Refer to the `Ably documentation <https://ably.com/docs/>`__ to learn more.
+For more information on migration, refer to the following:
+
+- `Ably Reference Architecture Guide <https://cdn.bfldr.com/2URK6TO/as/nchqb9kvw639qrp8cggb3/MongoDB__Ably_Reference_Architecture_Guide>`__
+- `Ably documentation <https://ably.com/docs/>`__
 
 Parse (Open Source)
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