[Doc] Move examples and further reorganize user guide (#18666)

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

docs/configuration/README.md

@@ -1,4 +1,9 @@
 # Configuration Options
 
-This section lists the most common options for running the vLLM engine.
-For a full list, refer to the [configuration][configuration] page.
+This section lists the most common options for running vLLM.
+
+There are three main levels of configuration, from highest priority to lowest priority:
+
+- [Request parameters][completions-api] and [input arguments][sampling-params]
+- [Engine arguments](./engine_args.md)
+- [Environment variables](./env_vars.md)

docs/configuration/env_vars.md

@@ -0,0 +1,12 @@
+# 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).
+
+```python
+--8<-- "vllm/envs.py:env-vars-definition"
+```