Add note on GitLab version requirement

doc/ci/examples/license_management.md

@@ -36,6 +36,8 @@ Due to implementation limitations we always take the latest License Management a
 
 ## Install custom project dependencies
 
+> Introduced in GitLab Ultimate 11.4.
+
 The `license_management` image already embeds many auto-detection scripts, languages, 
 and packages. Nevertheless, it's almost impossible to cover all cases, for all projects.
 That's why sometimes it's necessary to install extra packages, or to have extra steps