Jenkins: Add status badge to ReadMe
# Elektra
[![Release](https://img.shields.io/github/release/ElektraInitiative/libelektra.svg)](https://github.com/ElektraInitiative/libelektra/releases/latest)
+[![Jenkins Build Status](https://img.shields.io/jenkins/t/https/build.libelektra.org/jenkins/job/libelektra/job/master.svg)](https://build.libelektra.org/jenkins/job/libelektra/job/master/lastBuild)
[![Travis Build Status](https://travis-ci.org/ElektraInitiative/libelektra.svg?branch=master)](https://travis-ci.org/ElektraInitiative/libelektra)
[![Cirrus Build Status](https://api.cirrus-ci.com/github/ElektraInitiative/libelektra.svg)](https://cirrus-ci.com/github/ElektraInitiative/libelektra)
[![Coverage Status](https://img.shields.io/coveralls/github/ElektraInitiative/libelektra.svg)](https://coveralls.io/github/ElektraInitiative/libelektra)
