web: added Tools link to firmware site

Tools/autotest/web-firmware/index.html

@@ -79,6 +79,8 @@ The software and hardware we provide is only for use in unmanned
 		     alt="Rover">APMrover2</a> - for land vehicles and boats<p>
 <a href="PX4IO"><img src="images/PX4IO.png" width="80"
 		     alt="PX4IO">PX4IO</a> - for the PX4IO board<p>
+<a href="Tools"><img src="images/tools.png" width="80"
+		     alt="Tools">Tools</a> - Build and development tools<p>
 
 <h2>Types of firmware available</h2>