Improve Table of Contents (ToC) formatting

[ElectricRCAircraftGuy]

Headings here look good, and are properly indented/nested in the ToC: http://localhost:4001/test-markup-syntax-highlighting/:

But here they look horrible for some reason: http://localhost:4001/ydotool-tutorial/

They aren't indented, but should be, and there are those weird lines before and after the "Quick summary" entry:

Investigate and identify why! And fix it.

[ElectricRCAircraftGuy]

I may have found it. It may be because I am skipping levels, going straight from a ## level 2 heading, to a #### level 4 heading:

## 2. Now, use it: have `ydotool` press <kbd>Windows</kbd> + <kbd>D</kbd>

#### Quick summary:

I bet that's it. See if you can make it work with headings skipping levels like this.

Here is the source file: https://github.com/ElectricRCAircraftGuy/ElectricRCAircraftGuy.github.io/blob/master/_posts/2023-06-17-ydotool-tutorial.md

View it raw, or edit it, to see the markdown.