Add design patterns readme files

[NaderZMahmoud]

• Implement Mediator Pattern with a software development team example.
• Implement Observer Pattern with a weather monitoring system example.
• Implement Prototype Pattern for cloning geometric figures.
• Implement Proxy Pattern for lazy loading images.
• Implement Singleton Pattern using a ChocolateBoiler example.
• Implement State Pattern using a Gumball Machine example.
• Implement Strategy Pattern with a Duck simulation example.
• Implement Template Method Pattern for beverage preparation and sorting.
• Implement Visitor Pattern with a housing unit example.