Fixed ReadmePanel destructor

It can now save the state of whether is is enabled or not in the
configuration file.

src/panels/readme/readmepanel.cpp

@@ -29,6 +29,12 @@ ReadmePanel::ReadmePanel ( QWidget* parent ) :
             this, SLOT(toggleView(bool)));
 }
 
+ReadmePanel::~ReadmePanel()
+{
+    ReadmePanelSettings::self()->save();
+}
+
+
 void ReadmePanel::toggleView(bool b)
 {
     ReadmePanelSettings::setEnabled(b);

src/panels/readme/readmepanel.h

@@ -19,7 +19,7 @@ class ReadmePanel : public Panel
 
 public:
     explicit ReadmePanel(QWidget* parent = nullptr);
-    ~ReadmePanel() override = default;
+    ~ReadmePanel() override;
     QSharedPointer<QAction> toggleViewAction;
 
 public Q_SLOTS: