Add 'About Porymap' window that contains useful information about the program

include/mainwindow.h

@@ -155,6 +155,8 @@ private slots:
 
     void on_toolButton_CollapseAll_clicked();
 
+    void on_actionAbout_Porymap_triggered();
+
 private:
     Ui::MainWindow *ui;
     TilesetEditor *tilesetEditor = nullptr;

include/ui/aboutporymap.h

@@ -0,0 +1,19 @@
+#ifndef ABOUTPORYMAP_H
+#define ABOUTPORYMAP_H
+
+#include <QMainWindow>
+
+namespace Ui {
+class AboutPorymap;
+}
+
+class AboutPorymap : public QMainWindow
+{
+public:
+    explicit AboutPorymap(QWidget *parent = nullptr);
+    ~AboutPorymap();
+private:
+    Ui::AboutPorymap *ui;
+};
+
+#endif // ABOUTPORYMAP_H