Fixed KindleGen detection on macOS

kindlecomicconverter/KCC_gui.py

@@ -858,7 +858,8 @@ class KCCGUI(KCC_ui.Ui_mainWindow):
                 if sys.platform.startswith('win'):
                     self.addMessage('Download it and place EXE in KCC directory.', 'error')
                 elif sys.platform.startswith('darwin'):
-                    self.addMessage('Install it using <a href="http://brew.sh/">Brew</a>.', 'error')
+                    self.addMessage('Install it using <a href="http://brew.sh/">Brew</a>: <i>brew cask install kindle-c'
+                                    'omic-creator</i>', 'error')
                 else:
                     self.addMessage('Download it and place executable in /usr/local/bin directory.', 'error')