Update comments around tensor_name

Signed-off-by: Kevin Chen <kevinch@nvidia.com>

Author: kevinch-nv

onnx/onnx.in.proto

@@ -257,6 +257,7 @@ message NodeDeviceConfigurationProto {
 // input or output tensor of a node.
 message ShardingSpecProto {
   // (Required) Identifies the input or output of the node that is being sharded.
+  // Required to match a name specified in the node's input or output list of ValueInfoProtos.
   // It is called `logical tensor` in subsequent descriptions.
   optional string tensor_name = 1;