Clarify that you can't change Jira summary and description (#2432)

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Co-authored-by: Katie Horne <katie.horne@semgrep.com>

Author: armchairlinguist

docs/semgrep-appsec-platform/jira.md

@@ -85,7 +85,11 @@ Issue types may have the same name, but a different Issue type ID. When creating
 
 ### Create mappings
 
-Optionally, you can customize the Jira field mappings and indicate which values they should be populated with. Semgrep can map from Jira fields to either Semgrep fields or static Jira fields. Currently, Semgrep supports the mapping of the following field types:
+Optionally, you can customize the Jira field mappings and indicate which values they should be populated with. Semgrep can map either Semgrep fields or static data to Jira fields. 
+
+Semgrep automatically populates the Jira **Reporter**, **Summary**, and **Description** fields. The issue **Reporter** is the integration user, and the **Summary** and **Description** contain information about the vulnerability. Click **See preview** to review the default mappings and any custom mappings you have created.
+
+Currently, Semgrep supports the mapping of the following field types:
 
 * Short texts
 * Paragraphs