Add "Contributing" section to top-level readme

copied https://github.com/MicrosoftEdge/Demos/blob/main/README.md

Author: Michael Hoffman

README.md

@@ -9,6 +9,25 @@ Welcome to the WebView2Samples repo.  This repo contains several types of sample
 *  Deployment samples - Samples that demonstrate deploying the WebView2 Runtime.  For more information, see [Deployment samples](https://docs.microsoft.com/microsoft-edge/webview2/samples/deployment-samples).
 
 
-#### Open Source repo
+## Contributing
 
-This repo follows the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).  See the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/).  Contact opencode@microsoft.com with any additional questions or comments.
+This project welcomes contributions and suggestions.  Most contributions require you to agree to a
+Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us
+the rights to use your contribution. For details, visit https://cla.opensource.microsoft.com.
+
+When you submit a pull request, a CLA bot will automatically determine whether you need to provide
+a CLA and decorate the PR appropriately (e.g., status check, comment). Simply follow the instructions
+provided by the bot. You will only need to do this once across all repos using our CLA.
+
+This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
+For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
+contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.
+
+
+## Trademarks
+
+This project may contain trademarks or logos for projects, products, or services. Authorized use of Microsoft 
+trademarks or logos is subject to and must follow 
+[Microsoft Trademark and Brand Guidelines](https://www.microsoft.com/en-us/legal/intellectualproperty/trademarks/usage/general).
+Use of Microsoft trademarks or logos in modified versions of this project must not cause confusion or imply Microsoft sponsorship.
+Any use of third-party trademarks or logos are subject to those third-party's policies.