add coverity scan badge

Author: DennisOSRM

index.html

@@ -33,6 +33,8 @@
       <td> <img src="https://travis-ci.org/DennisOSRM/Project-OSRM.png?branch=develop" alt="Build Status" /></b> </td>
     </tr>
     <tr>
+      <td> <a href="https://scan.coverity.com/projects/183">Coverity Scan</a> (develop) </td>
+      <td><img alt="Coverity Scan Build Status" src="https://scan.coverity.com/projects/183/badge.svg"/></td>
       <td> LUAbind port (master) </td>
       <td> <img src="https://travis-ci.org/DennisOSRM/luabind.png?branch=master" alt="Build Status" /></b> </td>
     </tr>