Improve and expand README documentation for NDArray examples

[NA-V10]

This PR improves the documentation for the nd4j-ndarray-examples module.

✔ What was added

Expanded README with a clear explanation of what an NDArray is

Updated usage guide for INDArray operations

Added runnable code examples for:

NDArray creation

Arithmetic operations

Reshaping and broadcasting

Included instructions for running the examples with Maven

Added expected output to help beginners understand behavior

✔ Why this is useful

The previous README was minimal and did not explain:

What NDArray is

How to run the examples

What each operation does

This PR makes the module easier to understand for:

Beginners learning DL4J

Students exploring NDArray fundamentals

New contributors who want to verify expected behavior

✔ Notes

No code changes — documentation only.

Safe update, no breaking changes.

[agibsonccc]

Try to clean this up and add back some more of the context that was there rather than just overriding something completely. I certainly don't mind better clarifying explanations of things though! Again thanks for the contributions!

[NA-V10]

Thank you for the review!
I’ll clean up the README and restore the previous context that was removed, integrating it with the new clarifications.
I’ll push an updated version soon.