Create update doc for 7.7

doc/update/7.6-to-7.7.md

+# From 7.6 to 7.7
+
+### 0. Stop server
+
+    sudo service gitlab stop
+
+### 1. Backup
+
+```bash
+cd /home/git/gitlab
+sudo -u git -H bundle exec rake gitlab:backup:create RAILS_ENV=production
+```
+
+### 2. Get latest code
+
+```bash
+sudo -u git -H git fetch --all
+sudo -u git -H git checkout -- db/schema.rb # local changes will be restored automatically
+```
+
+For GitLab Community Edition:
+
+```bash
+sudo -u git -H git checkout 7-7-stable
+```
+
+OR
+
+For GitLab Enterprise Edition:
+
+```bash
+sudo -u git -H git checkout 7-7-stable-ee
+```
+
+### 3. Update gitlab-shell
+
+```bash
+cd /home/git/gitlab-shell
+sudo -u git -H git fetch
+sudo -u git -H git checkout v2.4.0
+```
+
+### 4. Install libs, migrations, etc.
+
+```bash
+sudo apt-get install libkrb5-dev
+
+cd /home/git/gitlab
+
+# MySQL installations (note: the line below states '--without ... postgres')
+sudo -u git -H bundle install --without development test postgres --deployment
+
+# PostgreSQL installations (note: the line below states '--without ... mysql')
+sudo -u git -H bundle install --without development test mysql --deployment
+
+# Run database migrations
+sudo -u git -H bundle exec rake db:migrate RAILS_ENV=production
+
+# Clean up assets and cache
+sudo -u git -H bundle exec rake assets:clean assets:precompile cache:clear RAILS_ENV=production
+
+# Update init.d script
+sudo cp lib/support/init.d/gitlab /etc/init.d/gitlab
+```
+
+### 5. Update config files
+
+#### New configuration options for `gitlab.yml`
+
+There are new configuration options available for [`gitlab.yml`](config/gitlab.yml.example). View them with the command below and apply them to your current `gitlab.yml`.
+
+```
+git diff origin/7-6-stable:config/gitlab.yml.example origin/7-7-stable:config/gitlab.yml.example
+```
+
+#### Change Nginx settings
+
+* HTTP setups: Make `/etc/nginx/sites-available/gitlab` the same as [`lib/support/nginx/gitlab`](/lib/support/nginx/gitlab) but with your settings
+* HTTPS setups: Make `/etc/nginx/sites-available/gitlab-ssl` the same as [`lib/support/nginx/gitlab-ssl`](/lib/support/nginx/gitlab-ssl) but with your setting
+
+#### Setup time zone (optional)
+
+Consider setting the time zone in `gitlab.yml` otherwise GitLab will default to UTC. If you set a time zone previously in [`application.rb`](config/application.rb) (unlikely), unset it.
+
+### 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 is complete!
+
+## Things went south? Revert to previous version (7.6)
+
+### 1. Revert the code to the previous version
+Follow the [upgrade guide from 7.5 to 7.6](7.5-to-7.6.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
+```
+If you have more than one backup *.tar file(s) please add `BACKUP=timestamp_of_backup` to the command above.