Move cli args docs to its own page (#18228) (#18264)

Signed-off-by: Trevor Royer <troyer@redhat.com>

docs/source/serving/serve_args.md

@@ -0,0 +1,47 @@
+(serve-args)=
+
+# Server Arguments
+
+The `vllm serve` command is used to launch the OpenAI-compatible server.
+
+## CLI Arguments
+
+The following are all arguments available from the `vllm serve` command:
+
+<!--- pyml disable-num-lines 7 no-space-in-emphasis -->
+```{eval-rst}
+.. argparse::
+    :module: vllm.entrypoints.openai.cli_args
+    :func: create_parser_for_docs
+    :prog: vllm serve
+    :nodefaultconst:
+    :markdownhelp:
+```
+
+## Configuration file
+
+You can load CLI arguments via a [YAML](https://yaml.org/) config file.
+The argument names must be the long form of those outlined [above](#serve-args).
+
+For example:
+
+```yaml
+# config.yaml
+
+model: meta-llama/Llama-3.1-8B-Instruct
+host: "127.0.0.1"
+port: 6379
+uvicorn-log-level: "info"
+```
+
+To use the above config file:
+
+```bash
+vllm serve --config config.yaml
+```
+
+:::{note}
+In case an argument is supplied simultaneously using command line and the config file, the value from the command line will take precedence.
+The order of priorities is `command line > config file values > defaults`.
+e.g. `vllm serve SOME_MODEL --config config.yaml`, SOME_MODEL takes precedence over `model` in config file.
+:::