Clean up example and add a note to emphasize the user API; Co-authored-by: Damian Rouson <rouson@lbl.gov>

Author: milancurcic

README.md

@@ -176,6 +176,9 @@ examples, in increasing level of complexity:
 2. [sine](example/sine.f90): Approximating a sine function
 3. [mnist](example/mnist.f90): Hand-written digit recognition using the MNIST dataset
 
+The examples also show you the extent of the public API that's meant to be
+used in applications, i.e. anything from the `nf` module.
+
 The MNIST example uses [curl](https://curl.se/) to download the dataset,
 so make sure you have it installed on your system.
 Most Linux OSs have it out of the box.

example/mnist.f90

@@ -1,7 +1,6 @@
 program mnist
-  use nf, only: dense, input, network
-  use nf_datasets_mnist, only: label_digits, load_mnist
-  use nf_optimizers, only: sgd
+
+  use nf, only: dense, input, network, sgd, label_digits, load_mnist
 
   implicit none
 

src/nf.f90

@@ -1,6 +1,8 @@
 module nf
+  !! User API: everything an application needs to reference directly
   use nf_datasets_mnist, only: label_digits, load_mnist
   use nf_layer, only: layer
   use nf_layer_constructors, only: conv2d, dense, input, maxpool2d
   use nf_network, only: network
+  use nf_optimizers, only: sgd
 end module nf