FTW is not available with MR abstractions enabled

Fixes #10520

v21.1/topology-follow-the-workload.md

@@ -13,6 +13,8 @@ In a multi-region deployment, follow-the-workload is the default behavior for ta
 
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 If read performance is your main focus for a table, but you want low-latency reads everywhere instead of just in the most active region, consider [Global Tables](global-tables.html) or [Follower Reads](topology-follower-reads.html).
+
+Note that if you start using the [multi-region SQL abstractions](multiregion-overview.html) for a database, CockroachDB will no longer provide the follow-the-workload behavior described on this page for that database.
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 ## Prerequisites