Added G-API Python instructions

G-API-Python-Bindings.md

@@ -0,0 +1,39 @@
+# Intro
+
+G-API is also available in OpenCV for Python. This page explains how to build and test G-API in Python.
+
+## Requirements
+
+* Python3+ with `numpy`
+* OpenVINO - for inference tests with OpenVINO backend;
+* [ONNX RT](Using-G-API-with-MS-ONNX-Runtime) - for inference tests with ONNX Runtime backend;
+* Working `videoio` module - built with either FFMPEG or [GStreamer] support - as some tests are using video files as input.
+
+## Building
+
+Use this CMake option to enable Python (make sure to include options for OpenVINO and ONNX RT if necessary):
+
+```bash
+$ cmake /path/to/opencv -DWITH_PYTHON=ON -DCMAKE_BUILD_TYPE=Release
+$ make -j8 opencv_python3
+```
+
+## Testing
+
+Setup environment:
+
+```bash
+$ export LD_LIBRARY_PATH=<path-to-opencv-build>/lib/:$LD_LIBRARY_PATH
+$ export PYTHONPATH=<path-to-opencv-build>/python_loader/:$PYTHONPATH
+$ export OPENCV_TEST_DATA_PATH=<path-to-opencv_extra>/testdata/
+$ export OPENCV_DNN_TEST_DATA_PATH=<path-to-opencv_extra>/testdata/dnn
+```
+
+Now run G-API tests:
+
+```bash
+$ cd <path-to-opencv-build>
+$ OPENCV_PYTEST_FILTER=test_gapi* python3 <path-to-opencv-root>/modules/python/test/test.py
+```
+
+