Update readme for dashboards 1.0.0 (#579)

Update RC state to GA state

Issues resolved:
#577

Signed-off-by: Anan Zhuang <ananzh@amazon.com>

README.md

@@ -2,9 +2,10 @@
 
 Hello!
 
-OpenSearch Dashboards is an open source search and analytics visualization derived from Kibana 7.10.2, and is currently in an RC state. While we're still in the process of getting set up, we are excited to build the best visualization platform for OpenSearch on the planet with you.
+OpenSearch Dashboards is an open source search and analytics visualization. We aim to to be the best community-driven platform and provide all the contributors a great open source experience.
+
+Feel free to take a look at what the community has been up to, and then head over to the [Project Board](https://github.com/opensearch-project/OpenSearch-Dashboards/projects) to track release targets, or jump in and [start opening issues](https://github.com/opensearch-project/OpenSearch-Dashboards/issues/new/choose) or [contributing](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/CONTRIBUTING.md).
 
-We officially began work on the new fork on January 21st, 2021.  Since then, we've been removing non-Apache 2.0 compliant code and doing a full rename of the project. Feel free to take a look at what we've been up to, and then head over to the [Project Board](https://github.com/opensearch-project/OpenSearch-Dashboards/projects) to track initial release targets, or jump in and [start opening issues](https://github.com/opensearch-project/OpenSearch-Dashboards/issues/new/choose) or [contributing](https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/CONTRIBUTING.md).
 
 ### Guiding Principles