[Doc][2/N] Reorganize Models and Usage sections (#11755)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

docs/source/serving/env_vars.md

@@ -0,0 +1,15 @@
+# Environment Variables
+
+vLLM uses the following environment variables to configure the system:
+
+```{warning}
+Please note that `VLLM_PORT` and `VLLM_HOST_IP` set the port and ip for vLLM's **internal usage**. It is not the port and ip for the API server. If you use `--host $VLLM_HOST_IP` and `--port $VLLM_PORT` to start the API server, it will not work.
+
+All environment variables used by vLLM are prefixed with `VLLM_`. **Special care should be taken for Kubernetes users**: please do not name the service as `vllm`, otherwise environment variables set by Kubernetes might conflict with vLLM's environment variables, because [Kubernetes sets environment variables for each service with the capitalized service name as the prefix](https://kubernetes.io/docs/concepts/services-networking/service/#environment-variables).
+```
+
+```{literalinclude} ../../../vllm/envs.py
+:end-before: end-env-vars-definition
+:language: python
+:start-after: begin-env-vars-definition
+```