Add EE package download information

doc/install/packages.md

+# GitLab EE Omnibus packages
+
+We have started to create [gitlab-omnibus packages](https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/README.md) for GitLab Enterprise Edition.
+The availability and functionality of these packages may be limited; please contact support@gitlab.com for more information.
+
+## GitLab 6.6 Enterprise Edition
+
+- Ubuntu 12.04 64-bit [gitlab_6.6.3-ee.omnibus-1.ubuntu.12.04_amd64.deb](https://downloads-packages.s3.amazonaws.com/2601c69af9247a47334c21cb9c9e4267d21eb8e7/gitlab_6.6.3-ee.omnibus-1.ubuntu.12.04_amd64.deb)