And move Windows instructions to the first section

Commands for Linux were get from
https://github.com/JetBrains/skiko/blob/78f227f19bd4cb811d34fbc2df7befb4f76be355/.github/workflows/ci.yml#L102

Except we use `libx11-dev` instead of `xvfb`. Tested on a new system
(but I performed commands in other order, so I am not completely sure
that they are all needed)