Mention drag & drop APK in README

For consistency with --help and manpage.

README.md

@@ -838,6 +838,7 @@ _<kbd>[Super]</kbd> is typically the <kbd>Windows</kbd> or <kbd>Cmd</kbd> key._
  | Inject computer clipboard text              | <kbd>MOD</kbd>+<kbd>Shift</kbd>+<kbd>v</kbd>
  | Enable/disable FPS counter (on stdout)      | <kbd>MOD</kbd>+<kbd>i</kbd>
  | Pinch-to-zoom                               | <kbd>Ctrl</kbd>+_click-and-move_
+ | Drag & drop APK file                        | Install APK from computer
 
 _¹Double-click on black borders to remove them._  
 _²Right-click turns the screen on if it was off, presses BACK otherwise._