To avoid confusion I seperated the `npm run build` and the `npm run dev` commands, beginners might get confused by each command being listed in the same list, thinking they need to run `npm run build` before Astro works properly.
Add `npm run preview` commands to all examples where they are missing
- Template is based on svelte components instead of react
- Bumps astro version to "^0.21.0-next.0" for portfolio-svelte template
Co-authored-by: Konstantinos Kostarellis <Konstantinos.Kostarellis@gmail.com>