Add nonzero() term under NumPy ndarray concept

[HarithaYerukonda]

Description

This PR adds a new term entry for the NumPy ndarray method nonzero().

• Includes description, syntax, example, and codebyte.
• Follows the Codecademy Docs term entry template and markdown standards.

Issue Solved

Closes #7867

Type of Change

• Adding a new entry
• Editing an existing entry (fixing a typo, bug, issues, etc)
• Updating the documentation

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.

[mamtawardhani]

Lookss good for a second review! 🚀

[Sriparno08]

Looks good, @HarithaYerukonda!

[github-actions]

👋 @HarithaYerukonda
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