Deprecate usage of `types` CI/CD configuration entry

doc/ci/yaml/README.md

@@ -70,7 +70,7 @@ There are a few reserved `keywords` that **cannot** be used as job names:
 | image         | no | Use docker image, covered in [Use Docker](../docker/README.md) |
 | services      | no | Use docker services, covered in [Use Docker](../docker/README.md) |
 | stages        | no | Define build stages |
-| types         | no | Alias for `stages` |
+| types         | no | Alias for `stages` (deprecated) |
 | before_script | no | Define commands that run before each job's script |
 | after_script  | no | Define commands that run after each job's script |
 | variables     | no | Define build variables |
@@ -130,6 +130,8 @@ There are also two edge cases worth mentioning:
 
 ### types
 
+> Deprecated, and will be removed in 10.0. Use [stages](#stages) instead.
+
 Alias for [stages](#stages).
 
 ### variables