Add comprehensive documentation for S3 tables and knowledge graphs

[Copilot]

This PR adds educational documentation to answer the questions "What are S3 tables?" and "What is knowledge graph?" as requested in the issue.

Changes Made

New Documentation Files

S3-Tables.md - Comprehensive guide covering:

• S3 as a data lake foundation with object storage concepts
• Common table formats (Parquet, Delta Lake, Apache Iceberg)
• Query engines for S3 data (Amazon Athena, Spark, Presto/Trino)
• Advantages of S3-based table storage patterns
• Common implementation patterns and learning resources

Knowledge-Graphs.md - In-depth explanation including:

• Core components: entities, relationships, and attributes
• Technical implementation using graph databases (Neo4j, Amazon Neptune)
• Real-world applications (search engines, recommendation systems, fraud detection)
• Advantages of graph-based data modeling
• Step-by-step guide for building knowledge graphs
• Examples from major tech companies (Google, Facebook, LinkedIn)

Updated README.md

Added a "Topics Covered" section that organizes the documentation by category:

• Data Engineering & Storage
• Data Science & AI

Each topic includes a brief description and links to the detailed documentation files.

Repository Alignment

The documentation maintains the repository's purpose as a personal learning journal while providing comprehensive, educational content that can serve as a reference for understanding these important technical concepts.

Fixes #27.

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