Add a note about maintenance mode to root README.md (#3895)

Author: Wovchena

CONTRIBUTING.md

@@ -1,5 +1,6 @@
 # How to Contribute Models to Open Model Zoo
 
+> [!NOTE]
 > Open Model Zoo is in maintenance mode as a source of models. Check out model tutorials in [Jupyter notebooks](https://github.com/openvinotoolkit/openvino_notebooks).
 
 We appreciate your intention to contribute model to the OpenVINO™ Open Model Zoo (OMZ). OMZ is licensed under the Apache\* License, Version 2.0. By contributing to the project, you agree to the license and copyright terms therein and release your contribution under these terms. Note that we accept models under permissive licenses, such as **MIT**, **Apache 2.0**, and **BSD-3-Clause**. Otherwise, it might take longer time to get your model approved.

README.md

@@ -1,4 +1,8 @@
 # [OpenVINO™ Toolkit](https://docs.openvino.ai/2023.0/index.html) - Open Model Zoo repository
+
+> [!NOTE]
+> Open Model Zoo is in maintenance mode as a source of models. Check out model tutorials in [Jupyter notebooks](https://github.com/openvinotoolkit/openvino_notebooks).
+
 This repository includes optimized deep learning models and a set of demos to expedite development of high-performance deep learning inference applications. Use these free pre-trained models instead of training your own models to speed-up the development and production deployment process.
 
 Intel is committed to the respect of human rights and avoiding complicity in human rights abuses, a policy reflected in the [Intel Global Human Rights Principles](https://www.intel.com/content/www/us/en/policy/policy-human-rights.html). Accordingly, by accessing the Intel material on this platform you agree that you will not use the material in a product or application that causes or contributes to a violation of an internationally recognized human right.