docs: add dataset prerequisite note before running the app

[Mohit-001-hash]

Overview

Added a missing documentation note reminding users to place the required dataset in the project root before running the application.

Description

• README.md

Core Motivation

To help users avoid setup issues caused by missing dataset directories before launching the application.

Proposed Changes

• Added a prerequisite note before the "Run the app" section.
• Directed users to the existing Placing the data section for proper dataset setup.
• Clarified that training and inference depend on the dataset being correctly placed.

Related Issue

Closes #None (just a documentation quick fix)

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation update (fixes or additions to docs)
• UI/UX improvement (changes to styling, templates, or frontend)
• Testing & Infrastructure (workflows, test scripts)

How Has This Been Tested?

• Checked changes locally
• Ran project test scripts

Screenshots (if applicable)

N/A

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.