feat: Improve README examples of stats/base/dists/gumbel

[olenkabilonizhka]

Resolves #1629

Description

What is the purpose of this pull request?

This pull request:

• Added example demonstration using functions in the README.
• Added the same demonstration example in examples/index.js

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves #1629

Questions

Any questions for reviewers of this pull request?

No.

Other

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• [x] Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[olenkabilonizhka]

Hi @kgryte ! Could you please describe the changes that need to do.