Added support + doc to Cusdis (#907)

### Prerequisites

Put an `x` into the box(es) that apply:

- [ ] This pull request fixes a bug.
- [ X] This pull request adds a feature.
- [ ] This pull request introduces breaking change.

### Description

Describe what this pull request achieves.

### Issues Resolved
This PR adds support for Cusdis commenting system
List any existing issues this pull request resolves.
Addresses  #896
### Checklist

Put an `x` into the box(es) that apply:

#### General

- [X] Describe what changes are being made
Added partial to call Cusdis JS + added ref to load partial + added
documentation
[X] Explain why and how the changes were necessary and implemented
respectively
  I started using Cusdis and I see there some demands for it.
- [X] Reference issue with `#<ISSUE_NO>` if applicable
 #896
#### Resources

- [ ] If you have changed any SCSS code, run `make release` to
regenerate all CSS files

#### Contributors

- [X] Add yourself to `CONTRIBUTORS.md` if you aren't on it already

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Co-authored-by: Luiz F. A. de Prá <luizdepra@users.noreply.github.com>