Update *Nested Docs* link in README.md

The old URL pointed to an archived Github repository. The new URL points to the docs page.

Author: franciscolourenco

README.md

@@ -101,7 +101,7 @@ See the [Collections](https://payloadcms.com/docs/configuration/collections) doc
 
 - #### Categories
 
-  A taxonomy used to group posts or projects together. Categories can be nested inside of one another, for example "News > Technology". See the official [Payload Nested Docs Plugin](https://github.com/payloadcms/plugin-nested-docs) for more details.
+  A taxonomy used to group posts or projects together. Categories can be nested inside of one another, for example "News > Technology". See the official [Payload Nested Docs Plugin](https://payloadcms.com/docs/plugins/nested-docs) for more details.
 
 ### Globals