Merge pull request #5500 from afshin/readme-triage

Update readme regarding maintenance

Author: Zsailer

README.md

@@ -11,6 +11,18 @@ computing.
 
 ![Jupyter notebook example](docs/resources/running_code_med.png "Jupyter notebook example")
 
+### Notice
+Please note that this repository is currently maintained by a skeleton crew of maintainers from the Jupyter community. We encourage users to transition to JupyterLab, where more immediate support can occur. Our approach moving forward will be:
+
+1. To maintain the security of the Jupyter Notebook. That means security-related issues and pull requests are our highest priority.
+2. To address JupyterLab [feature parity issues](https://github.com/jupyterlab/jupyterlab/issues?q=is%3Aopen+is%3Aissue+label%3A%22tag%3AFeature+Parity%22). As part of this effort, we are also working on a better [notebook-only experience](https://github.com/jupyterlab/jupyterlab/issues/8450) in JupyterLab for users who prefer the UI of the classic Jupyter Notebook.
+3. To be responsive to the hard work of community members who have opened pull requests. We are triaging these PRs. We cannot support or maintain new features at this time, but we welcome security and other sustainability fixes.
+
+If you have an open pull request with a new feature or if you were planning to open one, please consider shipping it as a [notebook extension](https://jupyter-notebook.readthedocs.io/en/stable/extending/) instead.
+
+##### Alternatives to contributing to `notebook`
+Additionally, please consider whether your contribution would be appropriate for either the underlying server for Jupyter front-ends, [jupyter_server](https://github.com/jupyter/jupyter_server) or in the [JupyterLab front-end](https://github.com/jupyterlab/jupyterlab).
+
 ### Jupyter notebook, the language-agnostic evolution of IPython notebook
 Jupyter notebook is a language-agnostic HTML notebook application for
 Project Jupyter. In 2015, Jupyter notebook was released as a part of