[Doc] Add environment variables doc (#519)

### What this PR does / why we need it?
Add environment variables doc.
---------

Signed-off-by: shen-shanshan <467638484@qq.com>

docs/source/index.md

@@ -45,6 +45,7 @@ faqs
 :maxdepth: 1
 user_guide/suppoted_features
 user_guide/supported_models
+user_guide/env_vars
 user_guide/release_notes
 :::
 

docs/source/user_guide/env_vars.md

@@ -0,0 +1,9 @@
+# Environment Variables
+
+vllm-ascend uses the following environment variables to configure the system:
+
+:::{literalinclude} ../../../vllm_ascend/envs.py
+:language: python
+:start-after: begin-env-vars-definition
+:end-before: end-env-vars-definition
+:::

vllm_ascend/envs.py

@@ -1,6 +1,31 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# This file is a part of the vllm-ascend project.
+#
+# This file is mainly Adapted from vllm-project/vllm/vllm/envs.py
+# Copyright 2023 The vLLM team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
 import os
 from typing import Any, Callable, Dict
 
+# The begin-* and end* here are used by the documentation generator
+# to extract the used env vars.
+
+# begin-env-vars-definition
+
 env_variables: Dict[str, Callable[[], Any]] = {
     # max compile thread num
     "MAX_JOBS":
@@ -31,6 +56,8 @@ env_variables: Dict[str, Callable[[], Any]] = {
     lambda: os.getenv("LLMDATADIST_SYNC_CACHE_WAIT_TIME", "5000")
 }
 
+# end-env-vars-definition
+
 
 def __getattr__(name: str):
     # lazy evaluation of environment variables