DOCSP-46402 added scheduled dashboard reports limitation (#690)

* added scheduled dashboard reports limitation

Author: kyuan-mongodb

source/dashboards/view-dashboard-data/scheduled-reports.txt

@@ -58,7 +58,11 @@ Limitations
 - For ``M2`` and higher tier {+clusters+}, you can create up to 100 
   scheduled reports per project.
 
-- At this time, scheduled reports can only be sent by email.
+- At this time:
+
+  - Scheduled reports can only be sent by email.
+  - If an entire dashboard takes more than five minutes to load, then
+    |charts-short| does not take a screenshot for scheduled reports.
 
 .. _create-scheduled-report: