Use core GitHub URL in contributing guidelines (home-assistant#41083)

Co-authored-by: springstan <[email protected]>

Author: gerard33

CONTRIBUTING.md

@@ -5,14 +5,14 @@ Everybody is invited and welcome to contribute to Home Assistant. There is a lot
 The process is straight-forward.
 
  - Read [How to get faster PR reviews](https://github.com/kubernetes/community/blob/master/contributors/guide/pull-requests.md#best-practices-for-faster-reviews) by Kubernetes (but skip step 0 and 1)
- - Fork the Home Assistant [git repository](https://github.com/home-assistant/home-assistant).
+ - Fork the Home Assistant [git repository](https://github.com/home-assistant/core).
  - Write the code for your device, notification service, sensor, or IoT thing.
  - Ensure tests work.
- - Create a Pull Request against the [**dev**](https://github.com/home-assistant/home-assistant/tree/dev) branch of Home Assistant.
+ - Create a Pull Request against the [**dev**](https://github.com/home-assistant/core/tree/dev) branch of Home Assistant.
 
 Still interested? Then you should take a peek at the [developer documentation](https://developers.home-assistant.io/) to get more details.
 
 ## Feature suggestions
 
 If you want to suggest a new feature for Home Assistant (e.g., new integrations), please open a thread in our [Community Forum: Feature Requests](https://community.home-assistant.io/c/feature-requests).
-We use [GitHub for tracking issues](https://github.com/home-assistant/home-assistant/issues), not for tracking feature requests.
+We use [GitHub for tracking issues](https://github.com/home-assistant/core/issues), not for tracking feature requests.