Launch-In-SITL.md

@@ -6,7 +6,14 @@ cd ardupilot_ws
 catkin init
 cd src
 ```
-Clone the reprository
+Clone the reprository into src
+
+Build the node with catkin_make:
+```shell
+cd ..
+catkin_make
+cd src
+```
 
 ## Launch SITL Instance
 Then, launch a SITL instance: