doc: image size

README.md

@@ -137,7 +137,7 @@ pdf2zh example.pdf -f "(CM[^RT].*|MS.*|.*Ital)" -c "(\(|\||\)|\+|=|\d|[\u0080-\u
 
 ### Interact with GUI
 
-![image](./docs/images/before.png)
+<img src="./docs/images/before.png" height="500"/>
 
 ```bash
 pdf2zh -i

docs/README_GUI.md

@@ -10,8 +10,8 @@ This subfolder provides the GUI mode of `pdf2zh`.
 
 ## Preview
 
-![image](./images/before.png)
-![image](./images/after.png)
+<img src="./images/before.png" height="500"/>
+<img src="./images/after.png" height="500"/>
 
 ## Maintainance