doc: add PoC badge

Author: HendrikReh

.gitignore

@@ -11,3 +11,6 @@ coverage/
 llm_providers.yaml
 .env.local
 /dist/
+/PROJECT_SUMMARY.md
+/RIG_RS_MIGRATION.PLAN.md
+/RELEASE_NOTES.md

README.md

@@ -5,6 +5,7 @@
 [![Rust Version](https://img.shields.io/badge/rust-1.70%2B-blue.svg)](https://www.rust-lang.org)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](https://github.com/HendrikReh/llm-guard/pulls)
 [![AI Coding Hackathon](https://img.shields.io/badge/AI%20Coding-Hackathon-purple)](https://maven.com/nila/ai-coding-accelerator)
+[![Proof of Concept](https://img.shields.io/badge/status-Proof_of_Concept-yellow)](https://github.com/HendrikReh/llm-guard)
 
 **LLM Provider Support:**
 [![OpenAI](https://img.shields.io/badge/OpenAI-412991?logo=openai&logoColor=white)](https://openai.com)