Link readme to blog handbook and markdown guide
What?
Pretty much simple and essential update to the README page, "Blog post" section:
- Asking the reader to check on the Blog Handbook
- Replacing old markdown guide with the new one, on Kramdown
Why?
This section deserves our effort to get much better on this section, which is a little confusing and incomplete. But this MR just adds the simplest update to the readme file.