feat: print usage when running patch without args (#124)

patch/src/main.rs

@@ -11,6 +11,23 @@ use std::time::Instant;
 
 fn main() {
     let mut args = std::env::args();
+    if args.len() < 4 {
+        eprintln!(
+            "Usage: {} <base> <new> <output>",
+            std::path::Path::new(&args.next().unwrap())
+                .file_name()
+                .unwrap()
+                .to_str()
+                .unwrap()
+        );
+        eprintln!("  base:   Path to the base file");
+        eprintln!("  new:    Path to the new file");
+        eprintln!("  output: Path to the output patch file");
+        eprintln!("");
+        eprintln!(" This is an internal tool for creating binary diffs.");
+        std::process::exit(1);
+    }
+
     args.next(); // skip program name
     let older = args.next().expect("path to base file");
     let newer = args.next().expect("path to new file");