Thanks for jjanzic's great work, based on it, add tesseract-ocr to try some ocr work

Docker image with python 3.6 and opencv 3.4

Usage:

docker run -it jjanzic/docker-python3-opencv python
>>> import cv2

Image tagged with :contrib contains docker image built with contrib modules

List of available docker tags:

• opencv-3.4.0 (latest branch)
• contrib-opencv-3.4.0 (contrib branch)
• opencv-3.3.0
• contrib-opencv-3.3.0
• opencv-3.2.0
• contrib-opencv-3.2.0