Update document to include benchmark CLI command

Author: shaahji

docs/source/reference/cli.rst

@@ -148,6 +148,17 @@ Delete Olive model cache stored in the cloud.
     :prog: olive
     :path: shared-cache
 
+Benchmark
+======================
+
+Run benchmarking using llm-eval.
+
+.. argparse::
+    :module: olive.cli.launcher
+    :func: get_cli_parser
+    :prog: olive
+    :path: benchmark
+
 Providing Input Models
 ======================