message: Add note about OTSU and TRIANGLE (comment sovrasov)
diff: @@ -2721,6 +2721,8 @@ or Triangle algorithm and uses it instead of the specified thresh . The function
  computed threshold value. Currently, the Otsu's and Triangle methods are implemented only for 8-bit
  images.
  +@note Input image should be single channel only in case of CV_THRESH_OTSU or CV_THRESH_TRIANGLE flags
  +
  @param src input array (multiple-channel, 8-bit or 32-bit floating point).
  @param dst output array of the same size and type and the same number of channels as src.
  @param thresh threshold value.
  