fix bug

src/main.rs

@@ -40,7 +40,7 @@ struct Args {
 	dit_length: u32,
 
 	/// Morse code frequency (defaults to center frequency) (Hz)
-	#[clap(short, long)]
+	#[clap(short = 'p', long)]
 	morse_freq: Option<f32>,
 
 	/// Number of times to repeat the output. Morse code is not repeated.