[DOC] Add instructions to install and run RayLLM backend locally

docs/run-backend-locally.md

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+# Install and Run RayLLM Backend Locally
+
+## Install latest Ray Serve
+
+```bash
+pip install ray[serve]
+```
+
+## Install RayLLM Backend from PR #149 branch (TODO: update link when PR merged)
+
+```bash
+git clone https://github.com/xwu99/ray-llm && cd ray-llm && git checkout support-vllm-cpu
+```
+
+Install for running on CPU device:
+```bash
+pip install -e .[backend] --extra-index-url https://download.pytorch.org/whl/cpu
+```
+
+Install for running on GPU device:
+```bash
+pip install -e .[backend]
+```
+
+## (Optional) Additional steps to install vllm from source for CPU device
+
+### Install GCC (>=12.3)
+
+```bash
+conda install -y -c conda-forge gxx=12.3 gxx_linux-64=12.3 libxcrypt
+```
+
+### Install latest vLLM (>= 0.4.1) on CPU
+
+```bash
+MAX_JOBS=8 VLLM_TARGET_DEVICE=cpu pip install -v git+https://github.com/vllm-project/vllm --extra-index-url https://download.pytorch.org/whl/cpu
+```
+
+## Test Run
+
+### Run on CPU device
+
+Start Ray from the directory of the code:
+
+```bash
+OMP_NUM_THREADS=32 ray start --head
+```
+
+To start serving:
+
+__Notice: Please change dtype to "bfloat16" for performance if you run on 4th generation Xeon Scalable (codename "Sapphire Rapids") or later CPU, otherwise use "float32" for compatibility.__
+
+```bash
+serve run ./serve_configs/cpu/meta-llama--Llama-2-7b-chat-hf.yaml
+```
+
+### Run on GPU device
+
+Start Ray from the directory of the code:
+
+```bash
+ray start --head
+```
+
+To start serving:
+
+__Notice: Please change "accelerator_type_a10" to match your GPU type__
+
+```bash
+serve run ./serve_configs/meta-llama--Llama-2-7b-chat-hf.yaml
+```
+
+### Query
+
+Export the endpoint URL:
+
+```bash
+export ENDPOINT_URL="http://localhost:8000/v1"
+```
+
+Send a POST request for chat completions:
+
+```bash
+curl -X POST $ENDPOINT_URL/chat/completions \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "meta-llama/Llama-2-7b-chat-hf",
+    "messages": [{"role": "system", "content": "You are a helpful assistant."}, {"role": "user", "content": "Hello!"}],
+    "temperature": 0.7
+  }'
+```
+
+### List Models
+
+Set the API base and key:
+
+```bash
+export OPENAI_API_BASE="http://localhost:8000/v1"
+export OPENAI_API_KEY="not-a-key"
+```
+
+List available RayLLM models:
+
+```bash
+rayllm models
+```
+
+## Caveat
+
+- The current working directory is where `ray start --head` runs, therefore if you use relative paths to define `models/*` files, the path should be relative to where Ray starts.
+- When switching Conda environments, you need to restart Ray.