Add documentation for full code quality report

Add bullet point for full code quality report
Clarify code quality MR widget comparison process
Add bullet point about downloading the JSON artifact
Add warning about code quality artifact expiration

doc/user/project/merge_requests/code_quality.md

@@ -260,11 +260,16 @@ GitLab.
 
 ## Code Quality reports
 
-Once the Code Quality job has completed, GitLab:
+Once the Code Quality job has completed:
 
-- Checks the generated report.
-- Compares the metrics between the source and target branches.
-- Shows the information right on the merge request.
+- The full list of code quality violations generated by a pipeline is available in the
+  Code Quality tab of the Pipeline Details page.
+- Potential changes to code quality are shown directly in the merge request.
+  The Code Quality widget in the merge request compares the reports from the base and head of the branch,
+  then lists any violations that will be resolved or created when the branch is merged.
+- The full JSON report is available as a
+  [downloadable artifact](../../project/pipelines/job_artifacts.html#downloading-artifacts)
+  for the `code_quality` job.
 
 If multiple jobs in a pipeline generate a code quality artifact, only the artifact from
 the last created job (the job with the largest job ID) is used. To avoid confusion,
@@ -276,6 +281,10 @@ Code Quality job in your `.gitlab-ci.yml` for the very first time.
 Consecutive merge requests will have something to compare to and the Code Quality
 report will be shown properly.
 
+These reports will only be available as long as the Code Quality artifact(s) required to generate
+them are also available. See
+[`artifacts:expire_in`](../../../ci/yaml/README.md#artifactsexpire_in) for more details.
+
 <!-- ## Troubleshooting
 
 Include any troubleshooting steps that you can foresee. If you know beforehand what issues