Document limitations on lines changed for summaries (#60574)

Co-authored-by: Joe Clark <31087804+jc-clark@users.noreply.github.com>

Author: chiph

content/copilot/responsible-use/pull-request-summaries.md

@@ -72,6 +72,10 @@ After you rate a summary as good or bad, you can provide written feedback by cli
 
 Currently, our team is aware that there are limitations to this feature. Many of them are expected in leveraging our {% data variables.product.prodname_copilot_short %} API; however, there are a few that are specific to {% data variables.copilot.copilot_for_prs %} which pertain to limited scope, longer processing times, and inaccurate responses. We also note that users should expect terms used in their PR to appear in the AI-generated summary. This feature has been subject to RAI Red Teaming and we will continue to monitor the efficacy and safety of the feature over time. For more information, see [Microsoft AI Red Team building future of safer AI](https://www.microsoft.com/en-us/security/blog/2023/08/07/microsoft-ai-red-team-building-future-of-safer-ai/) on the Microsoft security blog.
 
+### Lines changed limits
+
+Files with more than 400 combined additions and deletions are excluded from summarization.
+
 ### Limited scope
 
 Because of capacity, we know that larger pull requests that reference 30 or more files will require more time to be processed thoroughly. We don't have an exact threshold currently, but have observed the first 30 files being accounted for and then any additional files being omitted from the summarization. We are working to address this current scope limitation.