Update docs for 6.3

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

doc/update/6.2-to-6.3.md

+# From 6.2 to 6.3
+
+## Requires version: 6.1 or 6.2
+
+### 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 6.3-stable
+```
+
+### 3. Update gitlab-shell
+
+```bash
+cd /home/git/gitlab-shell
+sudo -u git -H git fetch
+sudo -u git -H git checkout v1.7.9 # Addresses multiple critical security vulnerabilities
+```
+
+### 4. Install additional packages
+
+```bash
+# Add support for lograte for better log file handling
+sudo apt-get install logrotate
+```
+
+### 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 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 6.2-stable:config/gitlab.yml.example 6.3-stable:config/gitlab.yml.example
+```
+
+* Make `/home/git/gitlab/config/gitlab.yml` same as https://github.com/gitlabhq/gitlabhq/blob/6.3-stable/config/gitlab.yml.example but with your settings.
+* Make `/home/git/gitlab/config/unicorn.rb` same as https://github.com/gitlabhq/gitlabhq/blob/6.3-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
+```
+* 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/6.3-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:
+
+    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 (6.2)
+
+### 1. Revert the code to the previous version
+Follow the [`upgrade guide from 6.1 to 6.2`](6.1-to-6.2.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
+```