message: Update info on QGroundControl Plan file format
  Update info on QGroundControl Plan file format in `Mission::import_mission_items_from_QGC_plan()`
diff: @@ -75,6 +75,7 @@ public:
  * @brief Imports QGC plan mission items.
  * @param[out] items Imported mission items from QGC plan.
  * @param qgc_plan_file Path of the QGC plan.
  + * @sa [QGroundControl Plan file format](https://dev.qgroundcontrol.com/en/file_formats/plan.html) (QGroundControl Dev Guide)
  * @return SUCCESS if successful in importing mission items, error code otherwise.
  */
  static Result import_mission_items_from_QGC_plan(mission_items_t &items,
  