Added preview feature description

README.md

@@ -10,6 +10,8 @@ A tool for converting high resolution images or textures with transparency to lo
 2. Choose the output resolution. For good results, the output resolution should be several times smaller than the input resolution. If the input image is a .SVG image, the tool converts it to a 4k input image to ensure the input resolution is high enough.
 3. Click the "generate" button to produce the output image. The output image is a .PNG image that can be downloaded.
 
+The quality of the output SDF can be previewed by hovering the cursor over the left panel that contains the input image. A circular area around the mouse shows how the SDF sprite will be rendered. If the left mouse button is pressed, the preview is zoomed by 200%.
+
 ## Settings
 
 |Setting|Description|