Add small comment at top of each file to show where in src code we are

src/cli.rs

@@ -1,3 +1,5 @@
+// src/cli.rs
+
 use std::path::PathBuf;
 
 use clap::Parser;

src/manip.rs

@@ -1,3 +1,5 @@
+// src/manip.rs
+
 use std::{collections::HashMap, fs, path::PathBuf};
 
 use log::error;