Update copyright notice in readme (#22)

MAINTAINERS.md

@@ -3,5 +3,5 @@
 ## Maintainers
 | Maintainer             | GitHub ID                                         | Affiliation |
 |------------------------|---------------------------------------------------|-------------|
-| David Cui              | [davidcui-amzn](https://github.com/davidcui-amzn) | Amazon      |
+| David Cui              | [davidcui1225](https://github.com/davidcui1225)   | Amazon      |
 | Joshua Li              | [joshuali925](https://github.com/joshuali925)     | Amazon      |

README.md

@@ -8,7 +8,7 @@ The OpenSearch Dashboards Visualizations enables you to use additional types of
 
 ## Documentation
 
-Please see our technical [documentation](https://docs-beta.opensearch.org/dashboards/gantt/) to learn more about its features.
+Please see our technical [documentation](https://opensearch.org/docs/dashboards/gantt/) to learn more about its features.
 
 ## Contributing
 
@@ -18,7 +18,7 @@ See [developer guide](DEVELOPER_GUIDE.md) and [how to contribute to this project
 
 If you find a bug, or have a feature request, please don't hesitate to open an issue in this repository.
 
-For more information, see [project website](https://opensearch.org/) and [documentation](https://docs-beta.opensearch.org/). If you need help and are unsure where to open an issue, try [forums](https://discuss.opendistrocommunity.dev/).
+For more information, see [project website](https://opensearch.org/) and [documentation](https://opensearch.org/docs/dashboards/gantt/). If you need help and are unsure where to open an issue, try [forums](https://discuss.opendistrocommunity.dev/).
 
 ## Code of Conduct
 
@@ -34,4 +34,4 @@ This project is licensed under the [Apache v2.0 License](LICENSE.txt).
 
 ## Copyright
 
-Copyright 2020-2021 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+Copyright OpenSearch Contributors. See [NOTICE](NOTICE.txt) for details.