Update readme for people like me who are new to NixOS

[Lyamc]

Just wanted to list a few ways I did things wrongly when setting it up for me.

0. (for the people like me who don't know, you should add the few lines for configuration.nix on how to enable flakes. Along with that you could add the build cache since it's the same category.
1. I got unrelated errors due to missing git in my configuration.nix
2. I could not run "nixos-rebuild switchbecause I had already createdflake.nixin/etc/nixos` and since I was missing git, nixos-rebuild it would always fail because it tried to do the flake so it wouldn't add git without me renaming flake.nix to something else and back after I had git.
3. I needed to also modify yourHost to pve
4. In the case where a GUI is used, a user will need more than 32GB available for all the compiling (think VMs)
5. I haven't a clue how to use the build cache. Pretty sure I added it. Doesn't really matter a lot to me but would to others.
6. sudo nixos-rebuild switch --flake /etc/nixos#pve once I had everything right and it takes a long time (you guys were not kidding about an intesive build process!)

Anyways, great work on the project, looking forward to future updates.