[Doc] : Update README with new sine wave example

[Advaitgaur004]

This PR updates the README.md to feature the new sine wave regression example from src2/main.c.

The previous Iris dataset example was quite basic. This new example better showcases cTensor's capabilities, including:

• A more complex model architecture (3 layers).
• Use of the Adam optimiser.
• A combined loss function (Huber + MAE).
• Implementation of gradient clipping.