Update Readme with scaling and limits details

AI Search (S1 Tier)

• Supports up to 24 billion documents across Basic, S1, S2, and S3 tiers.
• On a newly created S1 service (in regions that support higher-capacity partitions), you can scale to 12 partitions at 160 GB each for a total of ~1.92 TB.
• While individual document chunks in the index are limited to ~16 MB, the effective average max document chunk size is in the index is ~88 KB based on max scale.
• In real-world usage (e.g., Simple Chat RAG), document chunks are typically around 34 KB.
• Assuming 20-page documents (~88 KB for each page aka chunk), you can index up to ~1.2 million Office files (PDF, Word, PowerPoint, etc.) per index (user or group).

⸻

Cosmos DB (Provisioned Throughput Mode)
• Container-Level Storage:
• Each container can scale to unlimited storage, distributed across logical partitions (each capped at 20 GB).
• Database-Level Storage:
• Databases with shared throughput have no fixed storage limit; you can add more containers and data as needed.
• Account-Level Limits:
• Up to 500 databases/containers per account.
• Each container supports unlimited storage, adhering to the 20 GB per logical partition constraint.