Update developer guide with the new create-eth workflow

[Pabl0cks]

Updating the workflow to backmerge scaffold-eth/scaffold-eth-2:main branch into scaffold-eth/create-eth:main branch.

Based on #12 guidelines

Closes #6

[technophile-04]

Thanks @Pabl0cks !! This is nice!! Added a couple comments

Also we should update this and point it to core-extension instead of RFC-extension:

create-eth/contributors/DEVELOPER-GUIDE.md

Line 32 in 5a891c3

It's highly recommended that you go through [RFC-extensions.md](RFC-extensions.md) to understand the template API to create extensions. We use a custom template API to allow extensions to modify any file inside the `templates/` folder. While flexible and powerful, it requires developers to understand how it works. It's JS based, so there's no new technology needed to understand and use it.

[Pabl0cks]

Thanks a lot for your review @technophile-04 and @carletex !! ♥

Just pushed the review tweaks and changed the "RFC-extensions" reference to "core-extensions" 🙌

[technophile-04]

I think this looks great! Thanks Pablo!!