Fix example with iterable

The old example throws this error; `PHP Fatal error:  Uncaught TypeError: Argument 1 passed to Symfony\Component\Console\Helper\ProgressBar::iterate() must be iterable, object given`

Author: peterjaap

components/console/helpers/progressbar.rst

@@ -105,9 +105,13 @@ which starts, advances and finishes the progress bar automatically::
 
     $progressBar = new ProgressBar($output);
 
-    // $iterable can be for example an array ([1, 2, 3, ...]) or a generator
-    // $iterable = function () { yield 1; yield 2; ... };
-    foreach ($progressBar->iterate($iterable) as $value) {
+    // $iterable can be for example an array ([1, 2, 3, ...])
+    foreach ($progressBar->iterate([1, 2, 3]) as $value) {
+        // ... do some work
+    }
+    // or a generator
+    // function iterable() { yield 1; yield 2; ... };
+    foreach ($progressBar->iterate(iterable()) as $value) {
         // ... do some work
     }