fix: Update link to plugin tutorial (#5862)

**What's the problem this PR addresses?**
The link in the readme to the documentation for creating a new plugin is
broken.
fixes #5861

...

**How did you fix it?**
Replace the link with a valid link to the documentation.

...

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README.md

@@ -221,7 +221,7 @@ Plugins can be developed by third-party entities. To use them within your applic
 
 ### Creating a new plugin
 
-To create your own plugin, please refer to the [documentation](https://yarnpkg.com/features/plugins).
+To create your own plugin, please refer to the [documentation](https://yarnpkg.com/advanced/plugin-tutorial).
 
 ## Generic packages