Add litellm-rust README

litellm-rust/README.md

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+# litellm-rust
+
+A Rust port of LiteLLM's Mistral OCR transform logic. One pure, shared core
+(`src/llms/...`, `src/pipeline.rs`) is exposed two ways:
+
+1. A Python extension module `litellm_rust` (via PyO3) — the SDK/proxy call this.
+2. A standalone axum HTTP server binary `litellm-rust-server` serving `POST /v1/ocr`.
+
+The transform modules are pure (no PyO3, no I/O), mirroring the Python
+`litellm/llms/` tree:
+
+- `src/llms/base_llm/ocr/transformation.rs` — `BaseOcrConfig` trait + serde
+  response types (`OcrResponse`, `OcrPage`, `OcrPageImage`, `OcrUsageInfo`,
+  `OcrPageDimensions`) and `OcrRequest`.
+- `src/llms/mistral/ocr/transformation.rs` — `MistralOcrConfig`.
+
+## Build the Python extension
+
+PyO3 is an optional dependency behind the `python` feature, so the server binary
+never links libpython.
+
+```bash
+# from inside litellm-rust/
+maturin develop --features python
+```
+
+Then from Python:
+
+```python
+import litellm_rust
+
+resp = litellm_rust.ocr(
+    "mistral-ocr-latest",
+    {"type": "document_url", "document_url": "https://example.com/doc.pdf"},
+    None,            # api_key (falls back to MISTRAL_API_KEY)
+    None,            # api_base (defaults to https://api.mistral.ai/v1)
+    {"include_image_base64": True},
+)
+# -> {"pages": [...], "model": ..., "document_annotation": ..., "usage_info": {...}, "object": "ocr"}
+```
+
+## Run the standalone server
+
+The binary builds without the `python` feature:
+
+```bash
+# from inside litellm-rust/
+PORT=8088 cargo run --bin litellm-rust-server
+```
+
+Example request:
+
+```bash
+curl -s http://localhost:8088/v1/ocr \
+  -H 'Content-Type: application/json' \
+  -d '{
+        "model": "mistral-ocr-latest",
+        "document": {"type": "document_url", "document_url": "https://example.com/doc.pdf"},
+        "include_image_base64": true
+      }'
+```
+
+`api_key` may be supplied in the body; if omitted, the server reads
+`MISTRAL_API_KEY` from the environment. `GET /health` returns `{"status":"ok"}`.
+
+## Dev
+
+```bash
+cargo fmt
+cargo clippy --all-targets -- -D warnings
+cargo clippy --lib --features python -- -D warnings
+cargo check --bin litellm-rust-server
+```