reindexing: add note about single index result

Author: marciw

manage-data/data-store/data-streams/reindex-tsds.md

@@ -13,6 +13,10 @@ products:
 
 Reindexing allows you to copy documents from an old [time series data stream (TSDS)](/manage-data/data-store/data-streams/time-series-data-stream-tsds.md) to a new one. All data streams support reindexing, but time series data streams require special handling due to their time-bound backing indices and strict timestamp acceptance windows.
 
+:::{important}
+When you reindex, the result is a single backing index of a new data stream.
+:::
+
 To reindex, follow the steps on this page.
 
 :::{note}