Comment out @import directives

[oskarkook]

Deleting the @import "./phoenix.css"; rule is not clear if you have not used Tailwind CLI before. Since installing this package is backwards-incompatible in this sense, I think it would be clearer to just comment out those lines, especially since the application will now not be able to use the classes in ./phoenix.css. The user will have a clearer understanding of what is going on, even later on, if they do not overlook the changes and commit them straight into the repo.

In comparison, the change to assets/js/app.js keeps the original behaviour for the application and is therefore not a "destructive" action.

[philipgiuliani]

TailwindCSS CLI 3.1 now has support for the @import directive: https://tailwindcss.com/blog/tailwindcss-v3-1#built-in-support-for-css-imports-in-the-cli