message: Update IR doc to clarify initializers are permitted as node inputs
diff: @@ -208,7 +208,7 @@ They have the following properties:
  Name|Type|Description
  |---|---|---|
  name|string|An optional name of the node, used for diagnostic purposes only.
  -input|string[]|Names of the values used by the node to propagate input values to the node operator. It must refer to either a graph input or a node output.
  +input|string[]|Names of the values used by the node to propagate input values to the node operator. It must refer to either a graph input or a graph initializer or a node output.
  output|string[]|Names of the outputs used by the node to capture data from the operator invoked by the node. It either introduces a value in the graph or refers to a graph output.
  op_type|string|The symbolic identifier of the operator to invoke.
  domain|string|The domain of the operator set that contains the operator named by the op_type.
  