Update notes for v0.50

Truck City v0.50 has just been released. This is the change log:

• Improvement: truck window cargo selection list width increased
• Improvement: lateral bar menu for factories and warehouses reordered so parking spot is the last item in the rotation
• Improvement: increased visibility of Alt mode icons
• Improvement: added sound effects to the typewritter effect in the tutorials
• Improvement: lateral bar popup menus repositioned so they are more visible
• Feature: added new Alt mode icons
• Bugfix: save menu now correctly shows information on files