docs: add local dataset setup guide to README (#180)

[DhruvrajSinhZala24]

Related Issues

• Resolves README lacks clear dataset setup instructions for new users #180

Description

This pull request introduces a new section to the repository README.md containing detailed instructions for obtaining and organizing the simulated datasets locally.
The lack of clear dataset setup guidance was identified as a barrier for new contributors to properly initialize the environment. These additions directly address that gap by providing concrete download steps, the expected directory structure, and quickstart commands for both training and evaluation.

Changes Included

• Added section "2.1 Getting the simulated datasets locally" to the README.md.
• Download Instructions: Documented explicit steps to fetch the necessary datasets from DeepLenseSim.
• Directory Layout: Detailed the expected data/Model_* directory layout for proper data ingestion by the models.
• Quickstart Commands: Provided out-of-the-box CLI commands for running the training and evaluation pipelines to streamline the onboarding experience.