Update alacritty package and related instructions to use TOML

[dorraj.]

While setting up Alacritty to use this beautiful theme, I received a warning about the use of the provided .yml file. As I understand it, this should be converted to the TOML format. I have made the necessary changes in my own ~/.config/alacritty/ directory and have confirmed that the changes I've made work properly. Therefore, I am willing to work on the issue and submit a PR, since it is a simple change.