文章中有一处代码有缺陷

文件地址：algorithm-pattern/introduction/quickstart.md

问题strStr，问题代码：

```
func strStr(haystack string, needle string) int {
if len(needle) == 0 {
return 0
}
....
}
```

如果子串长度为0的话返回0有歧义，误认为子串起始地址为0，我觉得改为负数之类的更好。

Open algorithm-pattern/introduction/quickstart.md and inspect the strStr example. Check how an empty needle is defined by the surrounding explanation or referenced problem, then clarify the returned value so it cannot be mistaken for a valid starting index. Update the example and verify the documented behavior is unambiguous.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.