zephyr: add script for running mcuboot tests

It's onerous to work through the tests in docs/testplan-zephyr.md by
hand. Add a script which takes the thinking out of it.

Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>
diff --git a/docs/testplan-zephyr.md b/docs/testplan-zephyr.md
index 58e9458..2f7e255 100644
--- a/docs/testplan-zephyr.md
+++ b/docs/testplan-zephyr.md
@@ -6,6 +6,10 @@
 At this time, however, the partitions are hardcoded in the Makefile
 targets to flash.
 
+Note that the script "run-tests.sh" in that directory is helpful for
+automating the process, and provides simple "y or n" prompts for each
+test case and expected result.
+
 ## Building and running.
 
 The tests are build using the various `test-*` targets in