Add minimal supported version for Duo Code Suggestions

doc/user/project/repository/code_suggestions/index.md

@@ -10,6 +10,9 @@ DETAILS:
 **Tier:** Premium, Ultimate
 **Offering:** GitLab.com, self-managed, GitLab Dedicated. GitLab Duo Pro required.
 
+NOTE:
+GitLab Duo Code Suggestions requires [GitLab 16.8](https://about.gitlab.com/releases/2024/01/18/gitlab-16-8-released/) and newer. Earlier GitLab versions not supported.
+
 > - [Introduced support for Google Vertex AI Codey APIs](https://gitlab.com/groups/gitlab-org/-/epics/10562) in GitLab 16.1.
 > - [Removed support for GitLab native model](https://gitlab.com/groups/gitlab-org/-/epics/10752) in GitLab 16.2.
 > - [Introduced support for Code Generation](https://gitlab.com/gitlab-org/gitlab/-/issues/415583) in GitLab 16.3.