Update docs

Author: SzabolcsGergely

include/depthai/pipeline/node/StereoDepth.hpp

@@ -388,6 +388,8 @@ class StereoDepth : public NodeCRTP<Node, StereoDepth, StereoDepthProperties> {
     /**
      * Free scaling parameter between 0 (when all the pixels in the undistorted image are valid)
      * and 1 (when all the source image pixels are retained in the undistorted image).
+     * On some high distortion lenses, and/or due to rectification (image rotated) invalid areas may appear even with alpha=0,
+     * in these cases alpha < 0.0 helps removing invalid areas.
      * See getOptimalNewCameraMatrix from opencv for more details.
      */
     void setAlphaScaling(float alpha);