Add OptiSim usage example to README

[mademind122333-jp]

This PR adds a “Usage Example” section in the README demonstrating how to use the optisim_selection method from the Selector library.

Changes include:

• Added a Python code snippet showing how to select a diverse subset using OptiSim.
• Included comments explaining each step.
• Improved documentation for new users to understand basic usage.

Optional future enhancements:

• Include other selection methods (maxmin_selection, diverse_subset_selection).
• Add visualization of selected points for 2D/3D datasets.

[mademind122333-jp]

Hello @mademind122333-jp,
I have completed the required changes and the issue has been resolved from my side.
Kindly review and approve the workflows so that the merge can proceed.
Please let me know if any further modifications are needed.
Thank you for your time and support!

[mademind122333-jp]

Hello @mademind122333-jp,
I have completed the required changes and the issue has been resolved from my side.
Kindly review and approve the workflows so that the merge can proceed.
Please let me know if any further modifications are needed.
Thank you for your time and support!