start directory for file chooser is ~/Desktop

arduino_timetable/gui.py

@@ -275,7 +275,7 @@ class Application(tk.Frame):
         ''' selecting a new excel file with scheduled_commands '''
         # open the file selection dialog
         opts = {
-            'initialdir': '~/',
+            'initialdir': '~/Desktop',
             'filetypes': [('Excel Files', '.xlsx')],
             'multiple': False}
         excel_file = tk.filedialog.askopenfilename(**opts)