Documentation improvement regarding markup directive

Hello,

Documentation says:

> i3bar supports Pango markup, allowing your format strings to specify font, color, size, etc. by setting the markup directive to "pango".

It took me a while to understand that the way to set up `markup` was to do

```ini
general {
colors = true
interval = 5
markup = "pango"
}
```

I think it could make sense to add `markup = "pango"` in the `Sample configuration` like it seems to be done for others settings.

I can send a PR, if agreed

Locate the documentation section containing the “Sample configuration” and compare its listed settings with the `general` configuration example in the issue. Add `markup = "pango"` to that sample, then review the rendered documentation to confirm the setting is shown consistently and clearly.

Written by the indexing model from the issue text.