CLI: display `cesium` available authentication method

I would call this method v1 since it’s harming other v1 clients implementations. I won’t make this change since I am not Ğcli maintainer. This would also change the interface already advertised a lot on the forum.

I red the implementation, and found curious to find the hiden cesium command on which this option is based on

src/main.rs

@@ -42,7 +42,7 @@ pub struct Args {
 	/// (eventually followed by derivation path)
 	#[clap(short, long)]
 	secret: Option<String>,
-	/// Secret key format (seed, substrate)
+	/// Secret key format (seed, substrate, cesium)
 	#[clap(short = 'S', long, default_value = SecretFormat::Substrate)]
 	secret_format: SecretFormat,
 	/// Address