Document filename link in Vulnerability Report's details section

doc/user/application_security/vulnerability_report/index.md

@@ -36,6 +36,7 @@ From the Vulnerability Report you can:
 
 - [Filter the list of vulnerabilities](#filter-the-list-of-vulnerabilities).
 - [View more details about a vulnerability](#view-details-of-a-vulnerability).
+- [View vulnerable source location](#view-vulnerable-source-location) (if available).
 - [View an issue raised for a vulnerability](#view-issues-raised-for-a-vulnerability).
 - [Change the status of vulnerabilities](#change-status-of-vulnerabilities).
 - [Export details of vulnerabilities](#export-vulnerability-details).
@@ -99,6 +100,16 @@ Selection behavior when using the Activity filter:
 To view more details of a vulnerability, select the vulnerability's **Description**. The
 [vulnerability's details](../vulnerabilities) page is opened.
 
+## View vulnerable source location
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/267509) in GitLab 13.10.
+
+Some security scanners output the filename and line number of a potential vulnerability. When
+that information is available, the vulnerability's details include a link to the relevant file,
+in the default branch.
+
+To view the relevant file, select the filename in the vulnerability's details.
+
 ## View issues raised for a vulnerability
 
 The **Activity** column indicates the number of issues that have been created for the vulnerability.