Make pre-commit auto format markdown lint failures

After setting up pre-commit and writing a new markdown page, I got a few markdown lint errors. Unlike making changes in python, these errors weren't automatically fixed, so I had to update them manually. We should make it so it's autoformatted, similar to how it's done in Python and Java.

```
run markdownlint.........................................................Failed
- hook id: markdownlint
- exit code: 1
```