Fix confusion about stage name

Also wrapped some long lines.

doc/user/application_security/index.md

@@ -203,14 +203,34 @@ An approval will be optional when a license report:
 - Contains no software license violations.
 - Contains only new licenses that are `approved` or unknown.
 
-<!-- ## Troubleshooting
+## Troubleshooting
 
-Include any troubleshooting steps that you can foresee. If you know beforehand what issues
-one might have when setting this up, or when something is changed, or on upgrading, it's
-important to describe those, too. Think of things that may go wrong and include them here.
-This is important to minimize requests for support, and to avoid doc comments with
-questions that you know someone might ask.
+### Getting error message `sast job: stage parameter should be [some stage name here]`
 
-Each scenario can be a third-level heading, e.g. `### Getting error message X`.
-If you have none to add when creating a doc, leave this section in place
-but commented out to help encourage others to add to it in the future. -->
+When including a security job template like [`SAST`](sast/index.md#configuration),
+the following error can be raised, depending on your GitLab CI/CD configuration:
+
+```
+Found errors in your .gitlab-ci.yml:
+
+* sast job: stage parameter should be unit-tests
+```
+
+This error appears when the stage (nammed `test`) of the included job isn't declared
+in `.gitlab-ci.yml`.
+To fix this issue, you can either:
+
+- Add a `test` stage in your `.gitlab-ci.yml`.
+- Change the default stage of the included security jobs. For example, with `SAST`:
+
+  ```yaml
+  include:
+    template: SAST.gitlab-ci.yml
+
+  sast:
+    stage: unit-tests
+  ```
+
+[Learn more on overriding the SAST template](sast/index.md#overriding-the-sast-template).
+All the security scanning tools define their stage, so this error can occur with
+all of them.