message: Add mention of official arch linux package
  Since Alacritty does not require the AUR anymore, its mention has been
  removed from the README.
  To make future changes simpler, the README has also been reworded so
  less changes are required for adding new operating systems.
diff: @@ -36,18 +36,17 @@ built from source.
  ## Installation
  -Instructions are provided for macOS and many Linux variants to compile Alacritty
  -from source. With the exception of Arch (which has a package in the AUR), Void Linux (in main repository) and
  -[NixOS](https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/misc/alacritty/default.nix), please first read the
  -[prerequisites](#prerequisites) section, then find the section for your OS, and
  -finally go to [building](#building) and [configuration](#configuration).
  +Some operating systems already provide binaries for Alacritty, for everyone else there are
  +instructions to compile Alacritty from source.
  +
  +For the manual installation, please first read the [prerequisites](#prerequisites) section,
  +then find the instructions for your OS, and finally go through the [building](#building)
  +and [configuration](#configuration) steps.
  ### Arch Linux
  ```sh
  -git clone https://aur.archlinux.org/alacritty-git.git
  -cd alacritty-git
  -makepkg -isr
  +pacman -S alacritty
  ```
  ### Debian/Ubuntu
  