fix readme.md in preprocess custom data

[detteiu0330]

Aruco preprocess does not work with latest version of OpenCV.
Added that it must be ver.4.6.0 or less.

[ivanvoid]

Wow this 3 hours of my life I will never get back.
Installation code:

# Get opencv source files 
wget -O opencv.zip https://github.com/opencv/opencv/archive/refs/tags/4.6.0.zip
unzip opencv.zip
# Create build directory
mkdir -p build && cd build
# Configure
cmake  ../opencv-4.6.0
# Build
cmake --build .

modifided code from here

Edit1: v4.6.0 also causes aruco.hpp error (for me)
Edit2: v 4.5.5, with it you can't just build project with
Cannot specify link libraries for target "calibration" which is not built by this project.