install: rewrite and reorganize

[pluiedev]

This is a biggie.

The way we used the word "official" was incredibly nebulous and unclear to the average person to the point that I felt driven to rewrite the entire page. Now, we only use the word "official" to mean packages built and distributed by the Ghostty project itself, while trustworthy packages built by e.g. Linux distros are explicitly named as such.

A whole laundry list of changes:

• Added the ghostty-bin package on Nixpkgs under macOS, plus an explanation of why we can't build Ghostty from source there

• Clarified that the Homebrew Cask and the ghostty-bin Nix package are merely repackagings of the .dmg, and should be perfectly safe and trustworthy

• Renamed the "Linux (Official)" section to just "Linux", and the "Linux (Community)" section to "Linux (Community Binaries)"

• Moved the instructions for using the AUR and the Nix flake to the "Prerelease Builds" page. That is the more logical place for them anyways, since an end user likely only uses them for building and installing tip releases

• Added much more detailed instructions on how to use the Flake (you can't trust people to magically know this)

• Added important caveats when it comes to running 3D-accelerated programs built with Nix on non-NixOS systems. It is so painfully common for people to install Ghostty on Nix on e.g. Fedora and then complain about how Ghostty fails to run there.

• Added a much longer warning to using community binaries. For the sake of safety.

• Fixed the links pointing to the Binary Releases page. If there's any I missed, let me know that I screwed up

• Removed openSUSE (done in a separate commit so that if they ever un-drop us, we could simply revert the commit)

[vercel]

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