examples: add note about offboard attitude

Author: julianoes

examples/offboard_attitude.py

@@ -1,5 +1,9 @@
 #!/usr/bin/env python3
 
+# Warning: Only try this in simulation!
+#          The direct attitude interface is a low level interface to be used
+#          with caution. On real vehicles the thrust values are likely not
+#          adjusted properly and you need to close the loop using altitude.
 
 import asyncio