Update Official Documentation link in README.md (#24)

<!-- Provide a general summary of your changes in the Title above -->
<!-- Apply the label "bug" or "enhancement" as applicable. -->

## Description / Motivation
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Simple update to README to update the link to the Official Documentation
to the new docs for the new open source SDK
<!-- Why is this change required? What problem does it solve? -->
Helps users/developers navigate to appropriate documentation
immmediately
<!-- If it fixes an open issue, please link to the issue here. -->


## Testing

- [x] The Unit & Intergration tests are passing.
- [x] I have added the necessary tests to cover my changes.

## Terms
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- [x] I agree to follow this project's [Code of
Conduct](CODE_OF_CONDUCT.md).

Author: dmealo

README.md

@@ -6,7 +6,7 @@ This repository contains source code for all Sitecore ASP.NET Core SDK packages
 
 ## Documentation and Community Resources
 
-- [Official Documentation](https://doc.sitecore.com/xp/en/developers/hd/latest/sitecore-headless-development/sitecore-asp-net-rendering-sdk.html)
+- [Official Documentation](https://doc.sitecore.com/xmc/en/developers/asp-net/latest/asp-net-core-sdk/sitecore-asp-net-core-sdk.html)
 - [StackExchange](https://sitecore.stackexchange.com/)
   - Be sure to tag your question with the `aspnetcoresdk` tag.
 - [Community Slack](https://sitecorechat.slack.com/messages/general)