docs: note BrowseChildren in gateway overview and client READMEs

clients/python/README.md

@@ -138,6 +138,25 @@ The methods return native Python types (`bool`, `datetime | None`, and a
 into the hierarchy without learning the underlying stub class. The
 service requires the `metadata:read` scope on the API key.
 
+### Browsing lazily
+
+For UI trees or OPC UA bridges, use `browse_children` to walk one level at a
+time instead of loading the full hierarchy with `discover_hierarchy`. Pass an
+empty request for root objects; subsequent calls set `parent_gobject_id`,
+`parent_tag_name`, or `parent_contained_path`. Filter fields match
+`DiscoverHierarchy`. Each response pairs `children` with `child_has_children` so
+you know which nodes to expand. See
+[Galaxy Repository](../../docs/GalaxyRepository.md#browsechildren) for full
+request and filter semantics.
+
+```python
+from zb_mom_ww_mxgateway.generated import galaxy_repository_pb2 as galaxy_pb2
+
+reply = await galaxy.browse_children(galaxy_pb2.BrowseChildrenRequest())
+for child, has_children in zip(reply.children, reply.child_has_children):
+    print(child.tag_name, "expand=" + str(has_children))
+```
+
 ### Watching deploy events
 
 `GalaxyRepositoryClient.watch_deploy_events` opens a server-streaming