docs: improve async component generators docs

[aralroca]

I have added an example that can now be done with SQLite and the async component generators of Brisa

import { Database } from "bun:sqlite";

const db = new Database("db.sqlite");

export default function MovieList() {
  return (
    <ul>
      <MovieItems />
    </ul>
  );
}

// Streaming HTML from SQLite query
async function* MovieItems() {
  for (const movie of db.query("SELECT title, year FROM movies")) {
    yield (
      <li>
        {movie.title} ({movie.year})
      </li>
    );
  }
}