[doc] update doc (#15740)

Signed-off-by: reidliu41 <reid201711@gmail.com>
Co-authored-by: reidliu41 <reid201711@gmail.com>

docs/README.md

@@ -2,19 +2,42 @@
 
 ## Build the docs
 
+- Make sure in `docs` directory
+
+```bash
+cd docs
+```
+
+- Install the dependencies:
+
 ```bash
-# Install dependencies.
 pip install -r ../requirements/docs.txt
+```
+
+- Clean the previous build (optional but recommended):
 
-# Build the docs.
+```bash
 make clean
+```
+
+- Generate the HTML documentation:
+
+```bash
 make html
 ```
 
 ## Open the docs with your browser
 
+- Serve the documentation locally:
+
 ```bash
 python -m http.server -d build/html/
 ```
 
-Launch your browser and open localhost:8000.
+This will start a local server at http://localhost:8000. You can now open your browser and view the documentation.
+
+If port 8000 is already in use, you can specify a different port, for example:
+
+```bash
+python -m http.server 3000 -d build/html/
+```