Document all of topgrade's steps

[Jackenmen]

I'm currently working on documenting all of the topgrade's steps, I think that the big variety is a very important selling feature of it and it could really use a list such as this one.

I'm listing all of the steps in the order they are done. As of now, I went through documenting all of the steps until, and including the Brew formulae update for Linux. Since this is still WIP, I'm keeping it a draft PR.

[SteveLauC]

Thanks for doing this, the links to the official documentations would be very useful.

[SteveLauC]

And, if you have any questions when working on this, feel free to ping me, I am willing to help:)

[Jackenmen]

Just to let you know, I have not abandoned this (I know it hasn't even been a week but I've been a bit silent :)), just didn't happen to have time to put into this. I added the rest of the Linux steps and macOS steps + done some rephrasals. The next few small sections will be DragonFly, FreeBSD, OpenBSD, and Android after which I'll be working on the big Unix section. Once that's complete, it seems that I'll be left with steps that get executed on all platforms which is also a big section.

I imagine that once the lists are complete, I'll want to add some indications as to how this list relates only to the default settings and I think that once it's merged, someone else could further improve this document and/or add another one explaining the applicability of cleanup and yes settings, and also any executable-specific settings. I'll probably also find some other minor things I can do touchups on. Adding sudo to the commands that do use it seems like one of the things that I'm likely going to improve on once I finish everything else as well.