Explain order of consolidated metadata keys in user guide

Author: lkluft

docs/user-guide/consolidated_metadata.rst

@@ -100,6 +100,14 @@ With nested groups, the consolidated metadata is available on the children, recu
    >>> consolidated['child'].metadata.consolidated_metadata
    ConsolidatedMetadata(metadata={'child': GroupMetadata(attributes={'kind': 'grandchild'}, zarr_format=3, consolidated_metadata=ConsolidatedMetadata(metadata={}, kind='inline', must_understand=False), node_type='group')}, kind='inline', must_understand=False)
 
+.. versionadded:: 3.1.1
+
+    The keys in the consolidated metadata are sorted prior to writing. Keys are
+    sorted in ascending order by path length, where a path is defined as a sequence
+    of strings joined by ``"/"``. For keys with the same path length, lexicographic
+    order is used to break the tie.  This behaviour ensures deterministic metadata
+    output for a given group.
+
 Synchronization and Concurrency
 -------------------------------