[Doctest] add installation doctest (#1179)

### What this PR does / why we need it?
Install doctest

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
CI passed

Related: https://github.com/vllm-project/vllm-ascend/pull/983

Co-authored-by: wangli <wangli858794774@gmail.com>

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>
Co-authored-by: wangli <wangli858794774@gmail.com>

docs/source/conf.py

@@ -23,6 +23,7 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
+import json
 import os
 
 # import sys
@@ -133,3 +134,7 @@ if READTHEDOCS_VERSION_TYPE == "tag":
 
 def setup(app):
     pass
+
+
+if __name__ == "__main__":
+    print(json.dumps(myst_substitutions))

docs/source/installation.md

@@ -246,7 +246,8 @@ for output in outputs:
 Then run:
 
 ```bash
-# export VLLM_USE_MODELSCOPE=true to speed up download if huggingface is not reachable.
+# Try `export VLLM_USE_MODELSCOPE=true` and `pip install modelscope`
+# to speed up download if huggingface is not reachable.
 python example.py
 ```