Document new Vulnerability Report vendor option in the Scanner filter

doc/user/application_security/vulnerability_report/index.md

@@ -49,7 +49,7 @@ You can filter the vulnerabilities table by:
 |:---------|:------------------|
 | Status   | Detected, Confirmed, Dismissed, Resolved. |
 | Severity | Critical, High, Medium, Low, Info, Unknown. |
-| Scanner  | [Available scanners](../index.md#security-scanning-tools). |
+| Scanner  | For more details, see [Scanner filter](#scanner-filter). |
 | Project  | For more details, see [Project filter](#project-filter). |
 | Activity | For more details, see [Activity filter](#activity-filter). |
 
@@ -61,12 +61,27 @@ To filter the list of vulnerabilities:
 1. Select values from the dropdown.
 1. Repeat the above steps for each desired filter.
 
-The vulnerability table is applied immediately. The vulnerability severity totals are also updated.
+After each filter is selected:
+
+- The list of matching vulnerabilities is updated.
+- The vulnerability severity totals are updated.
 
 The filters' criteria are combined to show only vulnerabilities matching all criteria.
 An exception to this behavior is the Activity filter. For more details about how it works, see
 [Activity filter](#activity-filter).
 
+## Scanner filter
+
+The scanner filter allows you to focus on vulnerabilities detected by selected scanners.
+
+When using the scanner filter, you can choose:
+
+- **All scanners** (default).
+- Individual GitLab-provided scanners.
+- Any integrated 3rd-party scanner. [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/229661) in GitLab 13.12.
+
+For details of each of the available scanners, see [Security scanning tools](../index.md#security-scanning-tools).
+
 ### Project filter
 
 The content of the Project filter depends on the current level:
@@ -89,8 +104,8 @@ Selection behavior when using the Activity filter:
 
 | Activity selection                  | Results displayed |
 |:------------------------------------|:------------------|
-|  All                                | Vulnerabilities with any Activity status (same as ignoring this filter). Selecting this will deselect any other Activity filter options. |
-|  No activity                        | Only vulnerabilities without either an associated Issue or that are no longer detected. Selecting this will deselect any other Activity filter options. |
+|  All                                | Vulnerabilities with any Activity status (same as ignoring this filter). Selecting this deselects any other Activity filter options. |
+|  No activity                        | Only vulnerabilities without either an associated Issue or that are no longer detected. Selecting this deselects any other Activity filter options. |
 |  With issues                        | Only vulnerabilities with one or more associated issues. Does not include vulnerabilities that also are no longer detected. |
 |  No longer detected                 | Only vulnerabilities that are no longer detected in the latest pipeline scan of the `default` branch. Does not include vulnerabilities with one or more associated issues. |
 |  With issues and No longer detected | Only vulnerabilities that have one or more associated issues and also are no longer detected in the latest pipeline scan of the `default` branch. |