Main: Use FILE_PATH as the environment variable for positional path

src/main.rs

@@ -76,6 +76,7 @@ impl Display for BranchType {
 #[command(author, version, about, long_about = None)]
 struct Arguments {
     /// An optional path write generated output to
+    #[arg(env = "FILE_PATH")]
     path: Option<String>,
 
     /// The number of characters to generate (not bytes)