docs: quote pip extras install examples (#512)

* docs: quote pip extras install examples

* docs: use double quotes for cross-shell portability

---------

Co-authored-by: nyxst4ck <289980115+nyxst4ck@users.noreply.github.com>

Author: nyxst4ck

README-zh.md

@@ -261,7 +261,7 @@ uv pip install open-dataflow
 
 ```shell
 pip install uv
-uv pip install open-dataflow[vllm]
+uv pip install "open-dataflow[vllm]"
 
 ```
 

README.md

@@ -278,7 +278,7 @@ If you want to use your own GPU for local inference, please use:
 
 ```shell
 pip install uv
-uv pip install open-dataflow[vllm]
+uv pip install "open-dataflow[vllm]"
 ```
 
 After installation, you can use the following command to check if dataflow has been installed correctly: