Update Contributor's Guide link in README.md (bevyengine#16592)

# Objective

- Fix outdated link in README.md

Perhaps the link name should be updated as well since the article is no
longer labelled as "Contributor's Guide"?
Either way better to avoid making users click twice.

Author: james-j-obrien

README.md

@@ -50,7 +50,7 @@ Before contributing or participating in discussions with the community, you shou
 
 ### Contributing
 
-If you'd like to help build Bevy, check out the **[Contributor's Guide](https://github.com/bevyengine/bevy/blob/main/CONTRIBUTING.md)**.
+If you'd like to help build Bevy, check out the **[Contributor's Guide](https://bevyengine.org/learn/contribute/introduction)**.
 For simple problems, feel free to [open an issue](https://github.com/bevyengine/bevy/issues) or
 [PR](https://github.com/bevyengine/bevy/pulls) and tackle it yourself!