Clarify private CodeQuality runner docs

Clarify required and optional builds directory configuration in
walkthrough steps.

doc/user/project/merge_requests/code_quality.md

@@ -161,6 +161,7 @@ to be consider, but may be preferable depending on your use case.
      --locked="false" \
      --access-level="not_protected" \
      --docker-volumes "/cache"\
+     --docker-volumes "/builds:/builds"\
      --docker-volumes "/var/run/docker.sock:/var/run/docker.sock" \
      --registration-token="<project_token>" \
      --non-interactive
@@ -173,8 +174,8 @@ to be consider, but may be preferable depending on your use case.
   in the previous step.
 
    ```shell
-   --builds-dir /tmp/builds
-   --docker-volumes /tmp/builds:/tmp/builds
+   --builds-dir "/tmp/builds"
+   --docker-volumes "/tmp/builds:/tmp/builds" # Use this instead of --docker-volumes "/builds:/builds"
    ```
 
    The resulting configuration: