Add rules for "Related" section

Considering two interesting rules

```yml
# Section "Related Articles"
- name: Content must have "Related Articles" section
  type: regex
  search: "## 🔗 Related Articles\n"
- name: Section "Related Articles" should contains at least 3 items
  type: regex
  search: "## 🔗 Related Articles\n\n(.*\n){3,}"
```