Add Quality badge to README

[skip ci]

README.md

 SonarQube Scanner 
 =========================
 [![Build Status](https://travis-ci.org/SonarSource/sonar-scanner-cli.svg?branch=master)](https://travis-ci.org/SonarSource/sonar-scanner-cli)
-[![Build status](https://ci.appveyor.com/api/projects/status/s3sg3fhui556v02o/branch/master?svg=true)](https://ci.appveyor.com/project/henryju/sonar-scanner-cli/branch/master)
+[![Build status](https://ci.appveyor.com/api/projects/status/s3sg3fhui556v02o/branch/master?svg=true)](https://ci.appveyor.com/project/henryju/sonar-scanner-cli/branch/master) [![Quality Gate Status](https://next.sonarqube.com/sonarqube/api/project_badges/measure?project=org.sonarsource.scanner.cli%3Asonar-scanner-cli&metric=alert_status)](https://next.sonarqube.com/sonarqube/dashboard?id=org.sonarsource.scanner.cli%3Asonar-scanner-cli)
 
-Official SonarQube Scanner used to start code analysis. Project configuration is read from a sonar-project.properties or passed on command line.
+Official SonarQube Scanner used to start code analysis. Project configuration is read from file `sonar-project.properties` or passed on command line.
 
-Documentation:
+Documentation
 http://docs.sonarqube.org/display/SCAN/Analyzing+with+SonarQube+Scanner
 
 Issue Tracker: