added example for expressions

Author: ANKUR DWIVEDI

README.md

@@ -260,7 +260,7 @@ var imageURL = imagekit.url({
 https://ik.imagekit.io/your_imagekit_id/tr:h-300,w-400,l-image,i-ik_canvas,bg-FF0000,w-300,h-100,l-end/img/sample-video.mp4
 ```
 
-**3. Arithmetic expressions In transformations**
+**4. Arithmetic expressions In transformations**
 
 ImageKit allows use of [arithmetic expressions](https://docs.imagekit.io/features/arithmetic-expressions-in-transformations) in certain dimension and position-related parameters, making media transformations more flexible and dynamic.