Qt: Add about dialog

src/duckstation-qt/aboutdialog.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "ui_aboutdialog.h"
+#include <QtWidgets/QDialog>
+
+class AboutDialog final : public QDialog
+{
+  Q_OBJECT
+
+public:
+  explicit AboutDialog(QWidget* parent = nullptr);
+  ~AboutDialog();
+
+private:
+  Ui::AboutDialog m_ui;
+
+};