Adds documentation about environments that limit background activities.

Closes #5275

apis/Google.Cloud.Diagnostics.AspNetCore/docs/index.md

@@ -24,6 +24,15 @@ The Google.Cloud.Diagnostics.AspNetCore package attempts to collect the filename
 entries are collected. However, to be able to collect this information PDBs must be included with
 the deployed code.
 
+# Note
+When running on environments that limit or disable CPU usage for background activities, for instance
+[Google Cloud Run](https://cloud.google.com/run/docs/tips/general#avoiding_background_activities), take care
+not to use the timed buffer options for any of Logging, Tracing or Error Reporting. Take into account
+that the timed buffer is used for all of these components by default so you will need to explicitly
+configure the buffers by using the `Google.Cloud.Diagnostics.AspNetCore.LoggerOptions`,
+`Google.Cloud.Diagnostics.Common.TraceOptions` and `Google.Cloud.Diagnostics.Common.ErrorReportingOptions` classes.
+Below you'll find examples of how to configure the buffers.
+
 # Getting started
 
 ## Initializing Google Diagnostics