Update templates for guidance

[kwkwan]

Metanorma PR checklist

• Breaking changes (list related PRs)
• Documentation update required (create task for this)
• External dependency introduced (documentation update need)
• Gem with native library introduced

[ronaldtse]

@kwkwan we need to document the guidance structure.

How do we provide guidance for "roles/associations"?

Right now the guidance.yaml file is only:

---
classes:
  - name: Building
    attributes: ...
  - name: LandUse
    attributes: ...

But it does not show how to provide guidance for associations.

[ronaldtse]

I have consulted @kwkwan -- the method to encode roles/associations is also under the attributes key, since attributes and roles/associations cannot share the same names, it is safe to encode them there. FYI @ReesePlews .