Fix SEO

Improve SEO. Now meta tags are generated with:

• title and description from _config.yml
• title of the article
• tags provided in the article.

An example SEO meta tag with all that would be this:

<meta name="description" content="Katarismo: building generative new worlds with LLMs; How to expose any private service outside your headscale network; tags: headscale tailscale wireguard internal"/>