paddingIndex documentation for TransposedConv2D (#561)

Author: Shashi456

Sources/TensorFlow/Layers/Convolutional.swift

@@ -462,6 +462,7 @@ public struct TransposedConv2D<Scalar: TensorFlowFloatingPoint>: Layer {
     @noDerivative public let strides: (Int, Int)
     /// The padding algorithm for convolution.
     @noDerivative public let padding: Padding
+    /// The paddingIndex property allows us to handle computation based on padding.
     @noDerivative public let paddingIndex: Int
 
     /// The element-wise activation function type.