Fix prefix and add info

backend/scripts/msg_dumper.py

@@ -14,7 +14,7 @@ Options:
     -l LIGIER_IP    The IP of the ligier [default: 127.0.0.1].
     -p LIGIER_PORT  The port of the ligier [default: 5553].
     -o LOG_DIR      Directory to dump the messages [default: logs].
-    -x PREFIX       Prefix for the log files [default: MSG,Born,Died].
+    -x PREFIX       Prefix for the log files [default: MSG].
     -h --help       Show this screen.
 
 """
@@ -47,6 +47,7 @@ class MSGDumper(Module):
         self.current_date = current_date_str()
         self.filename = self.prefix + ".log"
         self.filepath = os.path.join(self.path, self.filename)
+        self.cprint("Logging to {}".format(self.filepath))
         self.fobj = open(self.filepath, 'a')
 
     def update_file_descriptor(self):