Update `research/utils/README.md` to add pointers to `research/optimization`.
# Utilities for federated learning research
This directory contains general utilities used by the other directories under
-`research/`, for things like writing output, constructing grids of experiments,
-configuration via command-line flags, etc.
+`research/`. Examples include utiiles for saving checkpoints, writing metrics to
+disk, and configuring experiments via command-line flags. For examples of
+federated learning experiments using these utilities, see the
+[`research/optimization`](https://github.com/tensorflow/federated/blob/master/tensorflow_federated/python/research/optimization)
+directory.
These utilities are not part of the TFF pip package, and should be considered
experimental. Utilities may be removed or changed at any time.
