Update extend-sentinel-across-workspaces-tenants.md

reverting back to 20, which is the actual limit. Adding best practice perf tip.
-------
cc: @yelevin

Author: austinmccollum

articles/sentinel/extend-sentinel-across-workspaces-tenants.md

@@ -88,7 +88,7 @@ You can then write a query across both workspaces by beginning with `unionSecuri
 <!-- Bookmark added for backward compatibility with old heading -->
 You can now include cross-workspace queries in scheduled analytics rules. You can use cross-workspace analytics rules in a central SOC, and across tenants (using Azure Lighthouse), suitable for MSSPs. Note these limitations:
 
-- You can include **up to 100 workspaces** in a single query.
+- You can include **up to 20 workspaces** in a single query. For good performance though, we recommend keeping it under 5.
 - You must deploy Microsoft Sentinel **on every workspace** referenced in the query.
 - Alerts generated by a cross-workspace analytics rule, and the incidents created from them, exist **only in the workspace where the rule was defined**. The alerts won't be displayed in any of the other workspaces referenced in the query.