perf(docs): add custom registration example to index page

[jason-capsule42]

Alaska Airlines Pull Request

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Summary:

Add custom registration example

Type of change:

Please delete options that are not relevant.

• [ ] New capability
• [ ] Revision of an existing capability
• [ ] Infrastructure change (automation, etc.)
• [x] Other (please elaborate)

Checklist:

• [x] My update follows the CONTRIBUTING guidelines of this project
• [x] I have performed a self-review of my own update

By submitting this Pull Request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Pull Requests will be evaluated by their quality of update and whether it is consistent with the goals and values of this project. Any submission is to be considered a conversation between the submitter and the maintainers of this project and may require changes to your submission.

Thank you for your submission!
-- Auro Design System Team

[blackfalcon]

:tada: This PR is included in version 3.5.8 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: