docs: add docs on extending zarr 3

jhamman · jhamman · commit 7afb5b1ab46b · 2024-12-29T16:14:39.000-07:00
diff --git a/docs/user-guide/index.rst b/docs/user-guide/index.rst
@@ -24,10 +24,10 @@ Advanced Topics
 
     performance
     consolidated_metadata
+    extending
     whatsnew_v3
     v3_todos
 
 
 .. Coming soon
     async
-    extending
