clients/README: link to CLIENT-CLI.md

Signed-off-by: Jussi Kukkonen <jkukkonen@google.com>

Author: jku

clients/README.md

@@ -1,3 +1,4 @@
-This directory contains test clients for the test suite: They are intended
-to help the development of the test suite itself (and act as examples for
-actual client implementations)
+This directory contains test clients for the test suite. They are implementations of the
+client-under-test [CLI protocol](../CLIENT-CLI.md) and are intended to help the development
+of the test suite itself and to act as examples for actual client-under-test
+implementations.