added build date of appimage as version; closes #48

src/gui_qt/main/mainwindow.py

@@ -1071,3 +1071,8 @@ class NMRMainWindow(QtWidgets.QMainWindow, Ui_BaseWindow):
     @QtCore.pyqtSlot(name='on_actionCreate_starter_triggered')
     def create_starter(self):
         make_starter(os.getenv('APPIMAGE'))
+
+    @QtCore.pyqtSlot(name='on_actionAbout_triggered')
+    def show_version(self):
+        from nmreval.version import __version__
+        QtWidgets.QMessageBox.about(self, 'Version', f'Build date of AppImage: {__version__}')