Use 2 spaces instead of 4 spaces (or tabs) in *.md

If you use **Spaces — 2**, you can indent lists:


However, if you try and do the same thing with **Tabs — 2 or 4**, indenting always results in code formatting:


So, 2 spaces gives the most flexibility, because you can do:

---

- list item
- another

AND:

- list item in code format
- another in code format

---

Like that:

---

```
- list item
- another

AND:

- list item in code format
- another in code format
```

---

This means `.editorconfig`s [like this](https://github.com/stealjs/steal/blob/master/.editorconfig) should look more like:

```
; Unix-style newlines
[*]
end_of_line = LF
indent_style = tab
indent_size = 4

[{*.json,*.yml,*.md}]
indent_style = space
indent_size = 2
```

(notice addition of `*.md`)