Clarify that OPTIMIZE is optional

Author: kbatuigas

modules/manage/pages/iceberg/iceberg-topics-databricks-unity.adoc

@@ -32,7 +32,10 @@ When you enable predictive optimization, you must also set the following configu
 SET spark.databricks.delta.liquid.lazyClustering.backfillStats=true;
 SET spark.databricks.delta.computeStats.autoConflictResolution=true;
 
--- Optionally trigger compaction and liquid clustering on an existing table
+/*
+Optionally trigger compaction and liquid clustering on an existing table.
+Run OPTIMIZE to check the effect of predictive optimization on the table.
+*/
 OPTIMIZE `<catalog-name>`.redpanda.`<table-name>`;
 ```
 ====