docs(readme): minor hotkey fix

Author: exwm

readme.md

@@ -274,7 +274,7 @@ A shortcuts reference can be toggled by clicking the scissor icon in the video c
 
 **Shift+C:** Toggle auto looping of currently selected marker pair.
 
-**Ctrl+Alt+X:** Toggle previewing crop in pop-out window.
+**Shift+X:** Toggle previewing crop in pop-out window.
 
   ![yt_clipper_crop_preview.png](https://raw.githubusercontent.com/exwm/yt_clipper/master/assets/image/yt_clipper_crop_preview_pop_out.png)