Update README.md

Added note for 24 FPS checkbox

README.md

@@ -29,3 +29,4 @@ You can decide the upscale quality to use. **X2** means the image/video will be
 When you're done with the parameters, click **Select files** to select multiple files to be upscaled or **Select folder** to upscale every image and video in that folder. You can also drag and drop files into the window.
 
 **NOTE**: Depending on your GPU and CPU, upscaling large videos can take very long. Video upscaling progress can be saved to be resumed after closing the app. If your PC shuts down while you're upscaling a very large video, worry not. The process will continue where you left of if you try to upscale the video again. Just be sure to not delete the generated files.
+Also note: The framerate that upscaled videos are encoded in is reported in the video header. A video may report a wrong frame rate and if this happens, the audio may be out of sync with the upscaled video. Most videos are 24 FPS, and so a checkbox has been provided to enforce that regardless of what the video header reports. Try it again with this box checked and the it might fix the sync issue.