docs: update reference results for c7i.xlarge × 2 placement group run

[levleontiev]

Closes the missing README update after PR #12 (tiktoken removal) was merged.

Changes

• Hardware updated: c7i.2xlarge single-host → 2 × c7i.xlarge, cluster placement group, eu-central-1
• Latency table: new two-host numbers (p50 decision 304 µs / proxy 302 µs / nginx 235 µs)
• Throughput table: 195 000 RPS for both simple and complex policies
• Removed tiktoken/LLM row (not supported)
• CPU pinning note removed (not relevant for two-host setup)