BLOG-48 docs: add README documentation for sitemap generator utility

sitemap/README.md

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+# Sitemap Generator
+
+A Python-based utility that automatically generates an XML sitemap for the blog website. The sitemap helps search engines discover and index the blog's content more efficiently.
+
+## Features
+
+- Automatically generates a sitemap.xml file following the [Sitemap Protocol](https://www.sitemaps.org/protocol.html)
+- Includes both static pages and dynamic blog post entries
+- Regularly updates the sitemap on a scheduled basis using cron jobs
+- Containerized for easy deployment
+
+## Requirements
+
+- Python 3.x
+- Docker (for containerized deployment)
+- Dependencies:
+  - pydantic
+  - requests
+
+## Configuration
+
+The sitemap generator uses the following environment variables:
+
+| Variable       | Description                                         | Default    |
+| -------------- | --------------------------------------------------- | ---------- |
+| `API_BASE_URL` | Base URL of the blog's API                          | (required) |
+| `FRONTEND_URL` | Base URL of the frontend website                    | (required) |
+| `STORAGE_PATH` | Path where the generated sitemap.xml will be stored | `./static` |
+
+## Usage
+
+### Local Execution
+
+1. Install the required dependencies:
+
+   ```bash
+   pip install -r requirements.txt
+   ```
+
+2. Set the environment variables:
+
+   ```bash
+   export API_BASE_URL=http://api.example.com
+   export FRONTEND_URL=http://www.example.com
+   ```
+
+3. Run the generator:
+
+   ```bash
+   python gen_sitemap.py
+   ```
+
+### Docker Deployment
+
+1. Build the Docker image:
+
+   ```bash
+   docker build -t blog-sitemap-generator .
+   ```
+
+2. Create a directory on the host to store the generated sitemap:
+
+   ```bash
+   mkdir -p /path/to/host/dir
+   touch /path/to/host/dir/sitemap.xml
+   ```
+
+3. Run the container:
+
+   ```bash
+   docker run -d \
+     -e API_BASE_URL=http://api.example.com \
+     -e FRONTEND_URL=http://www.example.com \
+     -v /path/to/host/dir/sitemap.xml:/app/static/sitemap.xml \
+     blog-sitemap-generator
+   ```
+
+## Scheduled Execution
+
+The sitemap is automatically generated according to the schedule defined in the `crontab` file:
+
+- Every day at 00:00, 08:00, and 16:00 (UTC)
+
+## File Structure
+
+- `gen_sitemap.py`: Main script that generates the sitemap
+- `requirements.txt`: Python dependencies
+- `crontab`: Cron job schedule configuration
+- `Dockerfile`: Container configuration for deployment
+- `README.md`: Documentation (this file)
+
+## Output
+
+The generator produces a standard XML sitemap at the specified `STORAGE_PATH` containing:
+
+- The homepage URL
+- The posts listing page URL
+- Individual post URLs with their last modification dates