Update src/nf/nf_layer_constructors.f90

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

Author: milancurcic

src/nf/nf_layer_constructors.f90

@@ -135,7 +135,7 @@ module function conv2d(filters, kernel_width, kernel_height, activation) result(
       !! Example:
       !!
       !! ```
-      !! use nf, only :: conv2d, layer
+      !! use nf, only :: conv, layer
       !! type(layer) :: conv2d_layer  
       !! conv2d_layer = conv2d(filters=32, kernel_width=3, kernel_height=3)
       !! ```