Add 6.0-to-6.2 update guide

doc/update/6.0-to-6.2.md

+# From 6.0 to 6.2
+
+# In 6.1 we remove a lot of deprecated code.
+# You should update to 6.0 before installing 6.1 or higher so all the necessary conversions are run.
+
+### Deprecations
+
+#### Global issue numbers
+
+As of 6.1 issue numbers are project specific. This means all issues are renumbered and get a new number in their url. If you use an old issue number url and the issue number does not exist yet you are redirected to the new one. This conversion does not trigger if the old number already exists for this project, this is unlikely but will happen with old issues and large projects.
+
+### 0. Backup
+
+It's useful to 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 latest code
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H git fetch
+sudo -u git -H git checkout 6-2-stable
+```
+
+
+### 3. Install additional packages
+
+```bash
+# Add support for lograte for better log file handling
+sudo apt-get install logrotate
+```
+
+### 4. Update gitlab-shell
+
+```bash
+cd /home/git/gitlab-shell
+sudo -u git -H git fetch
+sudo -u git -H git checkout v1.7.1
+```
+
+### 5. 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 migrate_iids RAILS_ENV=production
+sudo -u git -H bundle exec rake assets:clean RAILS_ENV=production
+sudo -u git -H bundle exec rake assets:precompile RAILS_ENV=production
+sudo -u git -H bundle exec rake cache:clear RAILS_ENV=production
+```
+
+### 6. Update config files
+
+TIP: to see what changed in gitlab.yml.example in this release use next command: 
+
+```
+git diff 6-1-stable:config/gitlab.yml.example 6-2-stable:config/gitlab.yml.example
+```
+
+* Make `/home/git/gitlab/config/gitlab.yml` same as https://github.com/gitlabhq/gitlabhq/blob/6-2-stable/config/gitlab.yml.example but with your settings.
+* Make `/home/git/gitlab/config/unicorn.rb` same as https://github.com/gitlabhq/gitlabhq/blob/6-2-stable/config/unicorn.rb.example but with your settings.
+* Copy rack attack middleware config
+
+```bash
+sudo -u git -H cp config/initializers/rack_attack.rb.example config/initializers/rack_attack.rb
+```
+* Uncomment `config.middleware.use Rack::Attack` in `/home/git/gitlab/config/application.rb`
+* Set up logrotate
+
+```bash
+sudo cp lib/support/logrotate/gitlab /etc/logrotate.d/gitlab
+```
+
+### 7. Update Init script
+
+```bash
+sudo rm /etc/init.d/gitlab
+sudo curl --output /etc/init.d/gitlab https://raw.github.com/gitlabhq/gitlabhq/6-2-stable/lib/support/init.d/gitlab
+sudo chmod +x /etc/init.d/gitlab
+```
+
+### 8. Start application
+
+    sudo service gitlab start
+    sudo service nginx restart
+
+### 9. Check application status
+
+Check if GitLab and its environment are configured correctly:
+
+    cd /home/git/gitlab
+    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 south? Revert to previous version (6.0)
+
+### 1. Revert the code to the previous version
+Follow the [`upgrade guide from 5.4 to 6.0`](5.4-to-6.0.md), except for the database migration 
+(The backup is already migrated to the previous version)
+
+### 2. Restore from the backup:
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:restore RAILS_ENV=production
+```