Doc: Update information about Qt Creator plugin wizard

After the switch to CMake.
Extends 29f3be1a6e

Change-Id: I626bc7393d290710d7e5d1f2907e6fa1f25a7d21
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

doc/qtcreatordev/examples/exampleplugin/example.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "example_global.h"
+
+#include <extensionsystem/iplugin.h>
+
+//! [namespaces]
+namespace Example {
+namespace Internal {
+//! [namespaces]
+
+//! [base class]
+class ExamplePlugin : public ExtensionSystem::IPlugin
+{
+    Q_OBJECT
+    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "Example.json")
+//! [base class]
+
+public:
+    ExamplePlugin();
+    ~ExamplePlugin();
+
+//! [plugin functions]
+    bool initialize(const QStringList &arguments, QString *errorString);
+    void extensionsInitialized();
+    ShutdownFlag aboutToShutdown();
+//! [plugin functions]
+
+//! [slot]
+private:
+    void triggerAction();
+//! [slot]
+};
+
+} // namespace Internal
+} // namespace Example