improve CLI usability (#4670)

closes #3308

README.md

@@ -4,12 +4,11 @@ UglifyJS 3
 UglifyJS is a JavaScript parser, minifier, compressor and beautifier toolkit.
 
 #### Note:
-- **`uglify-js@3` has a simplified [API](#api-reference) and [CLI](#command-line-usage)
-  that is not backwards compatible with [`uglify-js@2`](https://github.com/mishoo/UglifyJS/tree/v2.x)**.
-- **Documentation for UglifyJS `2.x` releases can be found [here](https://github.com/mishoo/UglifyJS/tree/v2.x)**.
-- `uglify-js` supports ECMAScript 5 and some newer language features.
-- To minify ECMAScript 2015 or above, you may need to transpile using tools like
-  [Babel](https://babeljs.io/).
+- `uglify-js` supports JavaScript and most language features in ECMAScript.
+- For more exotic parts of ECMAScript, process your source file with transpilers
+  like [Babel](https://babeljs.io/) before passing onto `uglify-js`.
+- `uglify-js@3` has a simplified [API](#api-reference) and [CLI](#command-line-usage)
+  that is not backwards compatible with [`uglify-js@2`](https://github.com/mishoo/UglifyJS/tree/v2.x).
 
 Install
 -------

bin/uglifyjs

@@ -260,9 +260,14 @@ if (paths.length) {
     });
     run();
 } else {
+    var timerId = process.stdin.isTTY && process.argv.length < 3 && setTimeout(function() {
+        print_error("Waiting for input... (use `--help` to print usage information)");
+    }, 1500);
     var chunks = [];
     process.stdin.setEncoding("utf8");
-    process.stdin.on("data", function(chunk) {
+    process.stdin.once("data", function() {
+        clearTimeout(timerId);
+    }).on("data", function(chunk) {
         chunks.push(chunk);
     }).on("end", function() {
         files = { STDIN: chunks.join("") };