Call out default Git depth in CI YAML docs

doc/ci/yaml/README.md

@@ -3525,8 +3525,8 @@ You can set them globally or per-job in the [`variables`](#variables) section.
 
 > Introduced in GitLab 8.9 as an experimental feature.
 
-CAUTION: **Caution:**
-May change in future releases or be removed completely.
+NOTE: **Note**:
+As of GitLab 12.0, newly created projects will automatically have a [default `git depth` value of `50`](../pipelines/settings.md#git-shallow-clone).
 
 You can specify the depth of fetching and cloning using `GIT_DEPTH`. This allows
 shallow cloning of the repository which can significantly speed up cloning for