Improve a readme example (#235)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

readme.md

@@ -327,15 +327,15 @@ Let's say you want to show the output of a child process in real-time while also
 
 ```js
 const execa = require('execa');
-const getStream = require('get-stream');
 
-const stream = execa('echo', ['foo']).stdout;
+const subprocess = execa('echo', ['foo']);
 
-stream.pipe(process.stdout);
+subprocess.stdout.pipe(process.stdout);
 
-getStream(stream).then(value => {
-	console.log('child output:', value);
-});
+(async () => {
+	const {stdout} = await subprocess;
+	console.log('child output:', stdout);
+})();
 ```