README: fix a typo s/has showed/has shown/

diff --git a/README b/README
index 0e0e0c8..1672722 100644 (file)
--- a/README
+++ b/README
@@ -23,7 +23,7 @@ A few conditions are required to create a decent effect:
      subtraction it is recommended to disable auto-gain in the camera, and
      avoid any artifact introduced by the power line frequency);
   3. the subject should enter the scene only after the background learning
-     phase has finished, i.e. after opencv_trail_effect has showed the preview
+     phase has finished, i.e. after opencv_trail_effect has shown the preview
      window.