Update notes for v0.53

Truck City v0.53 has just been released. This is the change log:

• Improvement: added several missing icons for factories, especially oil and space related
• Improvement: loading port construction menu now shows factory icons

• Improvement: production window now shows factory icons

• Bugfix: in the Map editor mode, save and load windows did not update after saving a map
• Bugfix: clicking while the loading screen was still visible is not allowed anymore
• Bugfix: fixed issue where the tutorial window might block clicks to the lateral bar