♻️(react) split fonts in a seperate CSS file

Fonts were de-facto included in the bundled dist/style.css file which
wasn't convenient in situations were consumers wanted to import fonts
by themselves.

packages/react/src/docs/installation.stories.mdx

@@ -53,6 +53,7 @@ Then, add these lines at the top of your main stylesheet file:
   dark
   format={false}
   code={`
+@import "@openfun/cunningham-react/fonts"; // Imports default fonts ( Roboto ). You can also import fonts by yourself.
 @import "@openfun/cunningham-react/style"; // Imports the default theme.
 @import "cunningham-tokens"; // Imports the file you just generated.
   `}