[IMP] website: make tips bioutifoul, and add moar tips

PURPOSE

Make digest email and tips more appealing. The goals of these tips are

  * to encourage the adoption of other apps (Did you know ?);
  * to make Odoo look more fun (Fun tips and tricks, young and dynamic style);
  * to show social proof and increase trust (emphasis on already existing
    projects / customers to);

SPECIFICATIONS

Add a tip about SEO.

LINKS

Task ID 2197417
PR odoo/odoo#51619

Co-Authored-By: Elisabeth Dickinson <edi@odoo.com>
Co-Authored-By: Thibault Delavallée <tde@odoo.com>