docs: improve README examples of `constants/float16` namespace

[vr-varad]

Resolves #1555 .

Description

What is the purpose of this pull request?

improve README examples of constants/float16 namespace

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves #1555

Questions

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No.

Other

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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

[vr-varad]

I've included a helpful example that demonstrates how float16 and its functions can be used effectively. Could you please review it whenever you have a chance? Your feedback would be much appreciated. Thanks! @kgryte @Planeshifter