[BUG] Typo in README.md file

There is a typo in `README.md` on line 74.

https://github.com/CodingGarden/learn-to-code-resources/blob/fae0baa9a27cf35e94a61a12cefae9c345db34a5/README.md?plain=1#L74

Change it to :point_down: 
```markdown
* [LeetCode](https://leetcode.com/)
```

#### Screenshot

![image](https://user-images.githubusercontent.com/74750414/174504156-5a223346-b9a8-490f-9fe2-b902de30d28f.png)
