Added 7.14 update docs

doc/update/7.13-to-7.14.md

+# Update from 7.13 to 7.14
+
+## Notice
+
+__GitLab CI 7.14 requires GitLab 7.12 or higher and GitLab Multi Runner 0.5.0 or higher
+
+### 1. Stop CI server
+
+    sudo service gitlab_ci stop
+
+### 2. Switch to your gitlab_ci user
+
+```
+sudo su gitlab_ci
+cd /home/gitlab_ci/gitlab-ci
+```
+
+### 3. Get latest code
+
+```
+git fetch
+git checkout 7-14-stable
+```
+
+### 4. Install libs, migrations etc
+
+
+```
+# Install nodejs dependency:
+sudo apt-get install nodejs
+
+# For MySQL users
+bundle install --without postgres development test --deployment
+
+# For Postgres users
+bundle install --without mysql development test --deployment
+
+# Run migrations
+bundle exec rake db:migrate RAILS_ENV=production
+```
+
+
+### 5. Start web application
+
+    sudo service gitlab_ci start