Improve comments in Autopilot

Issue: https://denyspopov.atlassian.net/browse/AZ-14
Type: Improvement

src/main.cpp

@@ -1,20 +1,24 @@
 #include <QCoreApplication>
 #include <QDebug>
-#include "az_mission.h"
+
 #include "az_drone_controller.h"
+#include "az_mission.h"
 
 int main(int argc, char *argv[])
 {
+    // This is needed to have main event loop and signal-slot events in the AzDroneController.
     QCoreApplication a(argc, argv);
 
     if (argc != 2) {
-        qCritical() << "Please give mission file as an argument\n";
+        qCritical() << "Please give mission JSON file as an argument.\n";
         return 1;
     }
 
+    // Reads mission from the JSON file which is given as command line option.
     AzMission mission(argv[1]);
     cout << mission;
 
+    // Launch a drone controller using the MAVSDK for ArduPilot-based flight controllers.
     AzDroneController droneController(mission);
     droneController.start();