Create README for notebooks directory

Added instructions for downloading and ingesting the Kaggle Chest X-Ray dataset in the README.

notebooks/README.md

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+# 📓 **Notebooks Directory**
+
+This directory contains the core machine learning experiments, including Exploratory Data Analysis (EDA) and the PyTorch DenseNet121 fine-tuning pipeline.
+
+**⚠️ Prerequisite:** Before executing these notebooks, you must download the 2GB Kaggle Chest X-Ray dataset into the project workspace. Because we use Google Colab for GPU training, follow the instructions below to ingest the data directly into your active Colab session.
+
+---
+
+## 🔑 **Step 1: Obtain Your Kaggle API Token**
+
+To download the dataset programmatically, you need a personal Kaggle authentication token:
+1. Log in to your account at [Kaggle.com](https://www.kaggle.com/).
+2. Click your **Profile Picture** in the top right corner and select **Settings**.
+3. Scroll down to the **API** section.
+4. Click **Create New Token**. 
+5. Copy the generated token string (it will look something like `KGAT_...`). Treat this string like a password.
+
+---
+
+## 📥 **Step 2: Ingest Data
+### a. Via Colab Terminal (Single Command)**
+
+Google Colab now provides free terminal access. You can download, extract, and clean up the entire dataset by copying and pasting a single chained command.
+
+1. On the far left sidebar of your Colab interface, click the **Terminal icon** (`>_`).
+2. Copy the following block of code.
+3. **Replace `"your_actual_token_here"`** with your real Kaggle token.
+4. Paste it into the Colab terminal and press Enter:
+
+```bash
+export KAGGLE_API_TOKEN="your_actual_token_here" && pip install -q kaggle && mkdir -p ../dataset && kaggle datasets download -d paultimothymooney/chest-xray-pneumonia -p ../dataset && unzip -q ../dataset/chest-xray-pneumonia.zip -d ../dataset && rm ../dataset/chest-xray-pneumonia.zip && echo "✅ Dataset successfully downloaded and extracted!"
+```
+### b. Local Shell (e.g. Ubuntu)
+Run the following command from the project's root directory.
+```bash
+chmod +x scripts/01_download_dataset.sh
+./scripts/01_download_dataset.sh
+```