Add the 6.8 CE to EE update guide

doc/update/6.8-ce-to-ee.md

+# From Community Edition 6.8 to Enterprise Edition 6.8
+
+This guide assumes you have a correctly configured and tested installation of GitLab Community Edition 6.8.
+If you run into any trouble or if you have any questions please contact us at support@gitlab.com.
+
+### 0. Backup
+
+Make a backup just in case things go south:
+(With MySQL, this may require granting "LOCK TABLES" privileges to the GitLab user on the database version)
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
+```
+
+### 1. Stop server
+
+    sudo service gitlab stop
+
+### 2. Get the EE code
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H git remote add ee https://gitlab.com/subscribers/gitlab-ee.git
+sudo -u git -H git fetch --all
+sudo -u git -H git checkout 6-8-stable-ee
+```
+
+### 3. Update config files
+
+* Make `/home/git/gitlab/config/gitlab.yml` same as /home/git/gitlab/config/gitlab.yml.example but with your settings.
+Note: Under LDAP settings fill in the `group_base` setting.
+* Make `/home/git/gitlab/config/unicorn.rb` same as /home/git/gitlab/config/unicorn.rb.example but with your settings.
+
+### 4. Install libs, migrations, etc.
+
+```bash
+cd /home/git/gitlab
+
+# MySQL
+sudo -u git -H bundle install --without development test postgres --deployment
+
+#PostgreSQL
+sudo -u git -H bundle install --without development test mysql --deployment
+
+sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
+sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS_ENV=production
+```
+
+### 5. Update Init script
+
+```bash
+sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
+sudo chmod +x /etc/init.d/gitlab
+```
+
+### 6. Start application
+
+    sudo service gitlab start
+    sudo service nginx restart
+
+### 7. Check application status
+
+Check if GitLab and its environment are configured correctly:
+
+    sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production
+
+To make sure you didn't miss anything run a more thorough check with:
+
+    sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
+
+If all items are green, then congratulations upgrade complete!
+
+## Things went wrong? Revert to previous version (Community Edition 6.8)
+
+### 1. Revert the code to the previous version
+```bash
+cd /home/git/gitlab
+sudo -u git -H git checkout 6-8-stable
+```
+
+### 2. Restore from the backup:
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:restore RAILS_ENV=production
+```