Better RSS feed

[sergiodxa]

Is your feature request related to a problem? Please describe.
Right now the feed only contains the title and date of the articles.

We need to add more content, I’m thinking of this idea of RSS as newsletter where you write content for the RSS that is not the content itself but a newsletter inviting the user to read your article.

Describe the solution you'd like
Add a key in the meta to support multi line text (with Slack-like MD support) and render it as the content of the RSS feed.