Link to old patch update guide now that we install workhorse with a raketask

[ci skip]

doc/update/patch_versions.md

@@ -44,6 +44,10 @@ sudo -u git -H git checkout v`cat /home/git/gitlab/GITLAB_SHELL_VERSION` -b v`ca
 
 ### 4. Update gitlab-workhorse to the corresponding version
 
+>**Note:**
+This new way to install GitLab workhorse was introduced with GitLab 8.15. If you
+are using an older version follow [this guide instead][oldguide].
+
 ```bash
 cd /home/git/gitlab
 
@@ -93,3 +97,5 @@ sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
 ```
 
 If all items are green, then congratulations upgrade complete!
+
+[oldguide]: https://gitlab.com/gitlab-org/gitlab-ce/blob/8-14-stable/doc/update/patch_versions.md