add recommended local environment

Author: tony-xlh

README.md

@@ -5,7 +5,7 @@ This project is to store [Dynamic Web TWAIN](https://www.dynamsoft.com/web-twain
 ### Local Development
 
 1. Download the docs template repo and the Web TWAIN docs repo with [download-dwt.sh](https://github.com/tony-xlh/misc/raw/refs/heads/main/build-docs/download-dwt.sh).
-2. Install Ruby and Jekyll.
+2. Install Ruby.
 3. Go to the docs' folder and install dependencies.
 
    ```bash
@@ -18,6 +18,8 @@ This project is to store [Dynamic Web TWAIN](https://www.dynamsoft.com/web-twain
    bundle exec jekyll serve -P 5555 --trace --host=0.0.0.0
    ```
 
+The recommended environment is Linux — for Windows users, WSL is recommended.
+
 ### License
 
 All documentation is available under the terms of [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/).