Update utililization directions on README

[manoelcampos]

Since now the project is a repository template, the way to use it is different and the README was accordingly updated.

• Adds information to make it clear the repository is a template.
• If the user just wants to create his/her own website, he/she just has to click the "Use this template" button, instead of creating a fork.
• Makes headings numbered to make it easier to follow the sections.

[mojavelinux]

Thanks for providing these updated instructions. As far as the content goes, I'm happy to merge this in.

We don't typically enable section numbering on READMEs in this organization, and I can't see how it is helping in this case. So I prefer to move forward without that change.

Btw, numbered is the legacy attribute name to enable section numbering. The attribute is now named sectnums. See https://docs.asciidoctor.org/asciidoc/latest/sections/numbers/#turn-on-section-numbers

[manoelcampos]

Section numbering removed

[mojavelinux]

Thanks!