Add keyboard shortcuts sample to readme

Author: davidchesnut

README.md

@@ -6,6 +6,7 @@ Office Add-ins PnP is a community driven effort that helps developers extend, bu
 
 | Date               | Name           | Description  |
 | ------------------ | -------------- | ------------ |
+| November 5, 2020   | [(Preview) Use keyboard shortcuts for Office add-in actions](https://github.com/OfficeDev/PnP-OfficeAddins/tree/master/Samples/excel-keyboard-shortcuts) | Shows how to set up a basic Excel add-in project that utilizes keyboard shortcuts. Currently, the shortcuts are configured to show and hide the task pane as well as cycle through colors for a selected cell. |
 | March 9, 2020         | [(preview) Manage ribbon and task pane UI, and run code on doc open](https://github.com/OfficeDev/PnP-OfficeAddins/tree/master/Samples/excel-shared-runtime-scenario) | This sample shows how to create contextual ribbon buttons that are enabled based on the state of your add-in. It also shows how to use the Office.js API to show or hide the task pane. This sample also demonstrates how to run code when the task pane is closed, such as on document open. |
 | January 29, 2020   | [Use a shared library to migrate your Visual Studio Tools for Office add-in to an Office web add-in](https://github.com/OfficeDev/PnP-OfficeAddins/tree/master/Samples/VSTO-shared-code-migration) | Provides a strategy for code reuse when migrating from VSTO Add-ins to Office Add-ins. |
 | November 12, 2019  | [Get OneDrive data using Microsoft Graph and msal.js in an Office Add-in](https://github.com/OfficeDev/PnP-OfficeAddins/tree/master/Samples/auth/Office-Add-in-Microsoft-Graph-React) | Learn how to build a Microsoft Office Add-in, as a single-page application (SPA) with no backend, that connects to Microsoft Graph, and access workbooks stored in OneDrive for Business to update a spreadsheet.  |