Add missing QRestAccessManager constructor documentation

Fixes: QTBUG-121859
Change-Id: Ie8d9033a8efe36767f47509afe1a46c788cb13ca
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit d5f3a9095bfc5e8b2725dd11a6fb4761f2a54027)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qrestaccessmanager.cpp

@@ -519,6 +519,14 @@ Q_LOGGING_CATEGORY(lcQrest, "qt.network.access.rest")
     \overload
 */
 
+/*!
+    Constructs a QRestAccessManager object and sets \a parent as the parent
+    object, and \a manager as the underlying QNetworkAccessManager which
+    is used for communication.
+
+    \sa networkAccessManager()
+*/
+
 QRestAccessManager::QRestAccessManager(QNetworkAccessManager *manager, QObject *parent)
     : QObject(*new QRestAccessManagerPrivate, parent)
 {