Add Python GPU renderer implementation example (#1493)

* Add Python GPU renderer implementation example

Signed-off-by: Michael Dolan <michdolan@gmail.com>

* Move to apps with README

Signed-off-by: Michael Dolan <michdolan@gmail.com>

Co-authored-by: Patrick Hodoul <patrick.hodoul@autodesk.com>
Co-authored-by: Rémi Achard <remiachard@gmail.com>

src/apps/pyociodisplay/README.md

@@ -0,0 +1,38 @@
+<!-- SPDX-License-Identifier: CC-BY-4.0 -->
+<!-- Copyright Contributors to the OpenColorIO Project. -->
+
+pyociodisplay
+=============
+
+**Work in progress**. Minimal image viewer implementation demonstrating use of 
+the OCIO GPU renderer in a Python application.
+
+Usage
+-----
+
+1. Install dependencies on ``PYTHONPATH``
+2. Run ``python pyociodisplay.py``
+3. Load image with ``File/Load image...`` menu item
+
+Dependencies
+------------
+
+* PyOpenColorIO
+* [OpenImageIO (Python bindings)](https://github.com/OpenImageIO/oiio)
+* [Imath (Python bindings)](https://github.com/AcademySoftwareFoundation/Imath)
+* ``pip install requirements.txt``
+  * [numpy](https://pypi.org/project/numpy/)
+  * [PyOpenGL](https://pypi.org/project/PyOpenGL/)
+  * [PySide2](https://pypi.org/project/PySide2/)
+
+Implementation notes
+--------------------
+
+* Assumes the ``OCIO`` environment variable is defined and pointing to a 
+  compatible OCIO config file.
+* Takes into account file and viewing rules, and may change the input color 
+  space and/or view automatically when a new image is loaded.
+* Exposure and gamma controls are dynamic parameters, driving uniforms in the 
+  generated shader program.
+* Specific channel views can be toggled with R, G, B, A keys, and the RGBA view 
+  restored with C.