Update broken link for mnist_transfer_cnn example in README.md

[gaikwadrahul8]

Hi, Team
I've identified broken link for mnist_transfer_cnn python example on this page and based on my understanding, the Keras team has removed this example from the Keras examples section.

To address this issue, I have temporarily updated the broken link with the mnist_transfer_cnn.py file located in the Python folder.

Moving forward, I suggest we consider two options:

• Remove the reference: We can remove the statement "It follows the procedure outlined in the Keras mnist_transfer_cnn example.".
• Replace with a similar example: We can replace the reference with a link to a relevant example on the MNIST dataset from a reputable source such as Medium or Towards Data Science. This would provide users with an alternative learning resource.

I appreciate your time and look forward to your feedback on the proposed solutions. Thank you.