Add missing doc strings for 4 methods under layout.py.

PiperOrigin-RevId: 442615805

tensorflow/dtensor/python/layout.py

@@ -190,6 +190,7 @@ def name(self) -> str:
     return self._name
 
   def is_remote(self) -> bool:
+    """Returns True if a Mesh contains only remote devices."""
     return not self._local_device_ids and self._global_device_ids.size > 0
 
   def host_mesh(self):
@@ -220,9 +221,11 @@ def host_mesh(self):
     return h_mesh
 
   def device_type(self) -> str:
+    """Returns the device_type of a Mesh."""
     return self._device_type
 
   def contains_dim(self, dim_name: str) -> bool:
+    """Returns True if a Mesh contains the given dimension name."""
     return dim_name in self._dim_dict
 
   def __contains__(self, dim_name: str) -> bool:
@@ -404,6 +407,7 @@ def from_proto(proto: layout_pb2.MeshProto) -> 'Mesh':
                 global_devices)
 
   def shape(self) -> List[int]:
+    """Returns the shape of the mesh."""
     return [self.dim_size(dim) for dim in self._dim_names]
 
   @property