Fix vulnerability chart docs

doc/user/application_security/security_dashboard/index.md

@@ -73,18 +73,31 @@ CSV file containing details of the resources scanned.
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/235558) in GitLab 13.6.
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/285476) in GitLab 13.10, options to zoom in on a date range, and download the vulnerabilities chart.
-> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/285477) in GitLab 13.11, date range slider to visualise data between given dates.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/285477) in GitLab 13.11, date range slider to visualize data between given dates.
 
-At the project level, the Security Dashboard displays a chart with the number of vulnerabilities over time.
-Access it by navigating to **Security & Compliance > Security Dashboard**. We display historical
-data up to 365 days. The chart's data is updated daily.
+A project's Security Dashboard displays a chart with the total number of vulnerabilities
+over time. It updates daily with up to 365 days of historical data. By default,
+it shows statistics for all vulnerability severities.
+
+To access the dashboard, from your project's home page go to **Security & Compliance > Security Dashboard**.
 
 ![Project Security Dashboard](img/project_security_dashboard_chart_v13_11.png)
 
-Filter the historical data by clicking on the corresponding legend name. The image above, for example, shows
-only the graph for vulnerabilities with **high** severity.
+### Filter the vulnerabilities chart
+
+To filter the chart by vulnerability severity, select the corresponding legend name.
+
+In the previous example, the chart shows statistics only for vulnerabilities of medium or unknown severity.
+
+### Customize vulnerabilities chart display
+
+To customize the view of the vulnerability chart, you can select:
+
+- A specific time frame by using the time range handles (**{scroll-handle}**).
+- A specific area of the chart by using the left-most icon (**{marquee-selection}**) then drag
+  across the chart. To reset to the original range, select **Remove Selection** (**{redo}**).
 
-To zoom in, select the left-most icon, then select the desired rangeby dragging across the chart. Select **Remove Selection** (**{redo}**) to reset to the original date range.
+### Download a copy of the vulnerabilities chart
 
 To download an SVG image of the chart, select **Save chart to an image** (**{download}**).