add doxygen mainpage

Author: lreiher

.gitignore

@@ -333,3 +333,5 @@ CATKIN_IGNORE
 .history
 
 # End of https://www.gitignore.io/api/ros,c++,linux,macos,python,pycharm,visualstudiocode
+
+!doc/mainpage.dox

doc/mainpage.dox

@@ -0,0 +1,17 @@
+/**
+
+\mainpage
+
+\htmlinclude manifest.html
+
+\b mqtt_client provides a ROS nodelet that enables connected ROS-based devices or robots to exchange ROS messages via an MQTT broker using the MQTT protocol. This works generically for arbitrary ROS message types.
+
+Please note that this is the Code API Documentation. Check out the <a href=https://github.com/ika-rwth-aachen/mqtt_client>GitHub repository</a> for more information on how to use the package, including a <i>Quick Start</i> guide.
+
+<ul>
+  <li><a href=files.html>Files</a></li>
+  <li><a href=annotated.html>Classes</a></li>
+  <li><a href=index-msg.html>Msg/Srv Documentation</a></li>
+</ul>
+
+*/