Correct message re: enabling logging

If the `v` key is not set to `true` in the configuration file, Arduino Create Agent prints a helpful message to the
terminal.

Previously this message instructed the user to enable logging via a `-v` command line flag. However, Arduino Create
Agent doesn't have a `-v` flag. The sole mechanism for controlling logging is the `v` key of the configuration file.

The instructions in the message are hereby corrected to specify the use of the configuration file.

main.go

@@ -320,7 +320,7 @@ func loop() {
 	}
 
 	if !*verbose {
-		log.Println("You can enter verbose mode to see all logging by starting with the -v command line switch.")
+		log.Println("You can enter verbose mode to see all logging by setting the v key in the configuration file to true.")
 		log.SetOutput(io.Discard)
 	}