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

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

docs/source/serving/engine_args.md

@@ -0,0 +1,25 @@
+(engine-args)=
+
+# Engine Arguments
+
+Below, you can find an explanation of every engine argument for vLLM:
+
+```{eval-rst}
+.. argparse::
+    :module: vllm.engine.arg_utils
+    :func: _engine_args_parser
+    :prog: vllm serve
+    :nodefaultconst:
+```
+
+## Async Engine Arguments
+
+Below are the additional arguments related to the asynchronous engine:
+
+```{eval-rst}
+.. argparse::
+    :module: vllm.engine.arg_utils
+    :func: _async_engine_args_parser
+    :prog: vllm serve
+    :nodefaultconst:
+```