Update link to release docs in README

[ci skip]

README.md

@@ -80,7 +80,7 @@ There are a lot of [third-party applications integrating with GitLab](https://ab
 ## GitLab release cycle
-For more information about the release process see the [release documentation](http://doc.gitlab.com/ce/release/).
+For more information about the release process see the [release documentation](https://gitlab.com/gitlab-org/release-tools/blob/master/README.md).
 ## Upgrading