What is the correct way of adding CSS or JS libraries as dependencies with Composer in Symfony2?

In the Symfony 2 docs it's said:

A bundle should not embed third-party libraries written in JavaScript, CSS, or any other language.

Then how should I do that? I want to install Twitter Bootstrap, DataTables, and many other things as dependencies using Composer. But the only way I can think of is creating a bundle and embedding them.

What is the correct way to do this?