Update help text

README.md

@@ -22,7 +22,7 @@ Options:
   -r, --recreate-cache           Recrate cache
   -i, --interactive              Interactive mode
   -l, --list                     List currencies
-  -L, --list-rates <LIST_RATES>  List currencies
+  -L, --list-rates <LIST_RATES>  List exchange rate for currency
   -h, --help                     Print help
 
 ```

src/main.rs

@@ -37,7 +37,7 @@ struct Cli
     #[arg(short, long)]
     list: bool,
 
-    /// List currencies
+    /// List exchange rate for currency
     #[arg(short = 'L', long = "list-rates")]
     list_rates: Option<String>,
 }