Add Jenkins integration docs

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

doc/integration/README.md

@@ -7,3 +7,4 @@ See the documentation below for details on how to configure these services.
 + [LDAP](ldap.md) Set up sign in via LDAP
 + [OmniAuth](omniauth.md) Sign in via Twitter, GitHub, and Google via OAuth.
 + [Slack](slack.md) Integrate with the Slack chat service
++ [Jenkins](jenkins.md) Integrate with the Jenkins CI

doc/integration/jenkins.md

+# Jenkins CI integration
+
+GitLab can be configured to interact with Jenkins
+
+Integration includes: 
+
+* Trigger Jenkins build after push to repo
+* Show build status on Merge Request page
+
+Requirements: 
+
+* Jenkins GitLab Hook plugin
+* git clone access for Jenkins from GitLab repo (via ssh key)
+
+## Jenkins
+
+1. Install GitLab Hook plugin
+2. Setup jenkins project
+
+![screen](jenkins/jenkins_project.jpg)
+
+
+## GitLab
+
+
+### Read access to repository 
+
+Jenkins need read access to GitLab repository. We already specified private key to use in Jenkins. Now we need to add public key to GitLab project
+
+![screen](jenkins/gitlab_deploy.png)
+
+
+### Jenkins service
+
+Now navigate to GitLab services page and activate Jenkins
+
+![screen](jenkins/gitlab_service.png)
+
+
+Done! Now when you push to GitLab - it will create build for Jenkins. 
+And also you will be able to see merge request build statuswith link to Jenkins build.
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