Order OSes by popularity and userbase.

[johnnymatthews]

There are several sections throughout the docs where we list different steps based on the readers operating system. For example: https://docs.entropy.xyz/reference/rust-testing-interface/#prerequisites

We should keep these OSes in a consistent order; either popularity/user-base, or alphabetical. It makes sense to me that we want most users to have to click as little as possible on the site. So let's order by popularity rather than the alphabet (sorry Arch users).