updated readme for several opencv_contrib modules (done by Gary)

[vpisarev]

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• [N/A] There is a reference to the original bug report and related work
• [N/A] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• [+] The feature is well documented and sample code can be built with the project CMake

[vpisarev]

Hello @garybradski, we noticed some changes that you've done in several opencv_contrib's READMEs. Our policy is to submit every change through pull request mechanisms. Also, "master" is not the branch that you should modify explicitly. It's supposed to be read-only branch that is currently automatically synchronized (in one direction) 'from' 4.x and will be synchronized 'from' 5.x after 5.0 is released.

If you agree with this version of changes, please, approve it.