[Doc]Add asynchronous engine arguments to documentation. (#3810)

Co-authored-by: Simon Mo <simon.mo@hey.com>
Co-authored-by: Roger Wang <136131678+ywang96@users.noreply.github.com>

docs/source/models/engine_args.rst

@@ -118,3 +118,19 @@ Below, you can find an explanation of every engine argument for vLLM:
 .. option:: --quantization (-q) {awq,squeezellm,None}
 
     Method used to quantize the weights.
+
+Async Engine Arguments
+----------------------
+Below are the additional arguments related to the asynchronous engine:
+
+.. option:: --engine-use-ray
+
+    Use Ray to start the LLM engine in a separate process as the server process.
+
+.. option:: --disable-log-requests
+
+    Disable logging requests.
+    
+.. option:: --max-log-len
+
+    Max number of prompt characters or prompt ID numbers being printed in log. Defaults to unlimited.
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