[Week 0] Challenge: "Day 5: If, Switch, 3항 연산자"

## 나의 Challenge
> If, Switch, 3항 연산자를 이용한 조건문의 이해와 활용

## 담당
> @llj72

## Guiding Questions
> If문과 Switch 문은 어떤 차이가 있을까?
> 문자를 조건문으로 사용하는 방법이 궁금하다

## Guiding Activities
> Hacking With Swift 를 통해 공부하기

## 새로 추가할 노드
> Day5.md

Review the repository's existing study-node structure, then use Hacking With Swift as the stated learning resource for the Day 5 topic. Add Day5.md covering If, Switch, and ternary operators, including the guiding questions about their differences and using characters in conditions; done means the new node is present and consistent with the other study materials.

Written by the indexing model from the issue text.