README.md: Add coverity logo

README.md

@@ -1,6 +1,6 @@
 ## PX4 Flight Control Stack and Middleware ##
 
-[![Build Status](https://travis-ci.org/PX4/Firmware.svg?branch=master)](https://travis-ci.org/PX4/Firmware)
+[![Build Status](https://travis-ci.org/PX4/Firmware.svg?branch=master)](https://travis-ci.org/PX4/Firmware) [![Coverity Scan](https://scan.coverity.com/projects/3966/badge.svg?flat=1)](https://scan.coverity.com/projects/3966?tab=overview)
 
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/PX4/Firmware?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)