QDirIterator docs: add a cool recursive file-finding snippet

This is one of the main use cases for QDirIterator, but it wasn't
obvious enough that it's possible.

Change-Id: Idae11cfe75dd0e16f1a960bba2470b1695d11241
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>

src/corelib/doc/snippets/code/src_corelib_io_qdiriterator.cpp

@@ -60,3 +60,12 @@ while (it.hasNext()) {
     // ...
 }
 //! [0]
+
+//! [1]
+QDirIterator it("/sys", QStringList() << "scaling_cur_freq", QDir::NoFilter, QDirIterator::Subdirectories);
+while (it.hasNext()) {
+    QFile f(it.next());
+    f.open(QIODevice::ReadOnly);
+    qDebug() << f.fileName() << f.readAll().trimmed().toDouble() / 1000 << "MHz";
+}
+//! [1]

src/corelib/io/qdiriterator.cpp

@@ -56,6 +56,10 @@
 
     \snippet code/src_corelib_io_qdiriterator.cpp 0
 
+    Here's how to find and read all files filtered by name, recursively:
+
+    \snippet code/src_corelib_io_qdiriterator.cpp 1
+
     The next() function returns the path to the next directory entry and
     advances the iterator. You can also call filePath() to get the current
     file path without advancing the iterator.  The fileName() function returns