title: How do I add opencv_contrib to a CMake project?
body: <p>I installed OpenCV 3.4 (C++) from source, using CMake.  I reinstalled it using <code>-D OPENCV_EXTRA_MODULES_PATH=&lt;path&gt;</code>.  I believe this reinstall properly installed opencv_contrib, though I am not positive.  Assume it did install properly.  I have a project that utilizes OpenCV, and I properly include the default OpenCV include directories (I do <code>include_directories(${OpenCV_INCLUDE_DIRS})</code>, after <code>find_package(OpenCV)</code>). If my C++ project properly finds a non-contrib opencv include file, is there anything more I have to do to get it to recognize an opencv contrib include file?  It's not finding it, but googling showed only an extra lib included in "target_link_libraries", but not an extra directory included for "include_directories".</p>