Add Rated SQL Kotlin Example to README for beginners

[sai-30624]

This pull request (ID: sai-30624) adds a “Rated SQL Kotlin Example” section to the Exposed README.

What This PR Adds:

• A minimal Kotlin/Exposed example demonstrating table creation, inserting data, and querying results
• Includes a Cities table and a Users table with sample data
• Demonstrates filtering queries such as:
  • Users in a specific city
  • Adults (age >= 18)
• Example output is included to show expected results

Expected Output:

Cities:
St. Petersburg
Munich

Users in St. Petersburg:
Andrey
Sergey

Adults:
Sergey
Eugene

Why This Change Matters:

• Helps new users quickly understand how to perform basic operations in Kotlin using Exposed
• Non-breaking documentation improvement
• Makes the README more beginner-friendly and practical

Author: sai-30624
Email: 2400030624@kluniversity.in