Add sonarcloud badge to README.md

Author: jimmysoda

README.md

@@ -2,6 +2,7 @@ pdal-c: PDAL C API
 ==================
 
 [![Build Status](https://travis-ci.com/Simverge/pdal-c.svg?branch=master)](https://travis-ci.com/Simverge/pdal-c)
+[![Quality Gate](https://sonarcloud.io/api/project_badges/measure?project=Simverge_pdal-c&metric=alert_status&branch=sonarcloud)](https://sonarcloud.io/project/issues?id=Simverge_pdal-c&branch=sonarcloud)
 
 *pdal-c* is a C API for the Point Data Abstraction Library ([PDAL](http:/github.com/PDAL/PDAL))
 and is compatible with PDAL 1.7 and later.