Clarify that a stage has to be added to run DAST in .gitlab-ci.yml

doc/user/application_security/dast/index.md

@@ -72,6 +72,13 @@ To include the DAST template:
    For more information about template versioning, see the
    [CI/CD documentation](../../../development/cicd/templates.md#latest-version).
 
+1. Add a `dast` stage to your GitLab CI stages configuration:
+
+    ```yaml
+    stages:
+      - dast
+    ```
+
 1. Add the template to GitLab, based on your version of GitLab:
 
    - In GitLab 11.9 and later, [include](../../../ci/yaml/README.md#includetemplate)

lib/gitlab/ci/templates/Security/DAST.latest.gitlab-ci.yml

+# To use this template, add the following to your .gitlab-ci.yml file:
+#
+# include:
+#   template: DAST.latest.gitlab-ci.yml
+#
+# You also need to add a `dast` stage to your `stages:` configuration. A sample configuration for DAST:
+#
+# stages:
+#   - build
+#   - test
+#   - deploy
+#   - dast
+
 # Read more about this feature here: https://docs.gitlab.com/ee/user/application_security/dast/
 
 # Configure the scanning tool through the environment variables.