Add version note to Activity filter feature's docs

doc/user/application_security/vulnerability_report/index.md

@@ -14,26 +14,6 @@ Critical, High, Medium, Low, Info, Unknown). Below this, a table shows each vuln
 
 ![Vulnerability Report](img/group_vulnerability_report_v13_9.png)
 
-You can filter which vulnerabilities display by:
-
-| Filter | Available Options |
-| --- | --- |
-| Status | Detected, Confirmed, Dismissed, Resolved |
-| Severity | Critical, High, Medium, Low, Info, Unknown |
-| Scanner | [Available Scanners](../index.md#security-scanning-tools) |
-| Project | Projects configured in the Security Center settings, or all projects in the group for the group level report. This filter is not displayed on the project level vulnerability report |
-| Activity | Vulnerabilities with issues and vulnerabilities that are no longer detected in the default branch |
-
-The Activity filter behaves differently from the other Vulnerability Report filters. The other filter options all OR together to show results from any vulnerability matching one of the filter criteria. With the Activity filter, the selected values form mutually exclusive sets to allow for precisely locating the desired vulnerability records. Additionally, not all options can be selected in combination. 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. |
-|  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. |
-
 Clicking any vulnerability in the table takes you to its
 [vulnerability details](../vulnerabilities) page to see more information on that vulnerability.
 
@@ -42,6 +22,32 @@ Hover over an **Activity** entry and select a link go to that issue.
 
 ![Display attached issues](img/vulnerability_list_table_v13_9.png)
 
+## Filter options
+
+You can filter which vulnerabilities display by:
+
+| Filter   | Available options |
+|:---------|:------------------|
+| Status   | Detected, Confirmed, Dismissed, Resolved |
+| Severity | Critical, High, Medium, Low, Info, Unknown |
+| Scanner  | [Available scanners](../index.md#security-scanning-tools). |
+| Project  | Projects configured in the Security Center settings, or all projects in the group for the group level report. This filter is not displayed on the project level vulnerability report. |
+| Activity | Vulnerabilities with issues and vulnerabilities that are no longer detected in the default branch. |
+
+### Activity filter
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/259255) in GitLab 13.9
+
+The Activity filter behaves differently from the other Vulnerability Report filters. The other filter options all OR together to show results from any vulnerability matching one of the filter criteria. With the Activity filter, the selected values form mutually exclusive sets to allow for precisely locating the desired vulnerability records. Additionally, not all options can be selected in combination. 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. |
+|  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. |
+
 Contents of the unfiltered vulnerability report can be exported using our [export feature](#export-vulnerabilities).
 
 You can also dismiss vulnerabilities in the table: