Add a hello world snippet in the frontpage

[leostera]

Perhaps we could add the tiny HTTP server there?

https://github.com/AbstractMachinesLab/caramel/blob/main/examples/practical.t/echo.ml

That I think showcases a few cool things (like the fact that we do type-checked messages). But maybe we want to add a variant or a record too to showcase the type system a little more?

Side-note: it would be epic to get LAM in good shape to run examples on the browser too. caramel.run really screams "online repl" 😂

[clsource]

It would be awesome to have a Hello Phoenix too.
As an example of how to do some basic Elixir/Phoenix coding with Caramel :)