CORD-1939: add unit test documentation

Change-Id: I7ce4bc0baf24e71732ad81952d42abb1db203d0a
(cherry picked from commit e683fe5da074ba6929f4c07856babef95cf90921)
diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index c4b39f2..91cd0c8 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -42,6 +42,7 @@
         * [GUI Internals](xos-gui/architecture/README.md)
             * [Module Strucure](xos-gui/architecture/gui-modules.md)
             * [Data Sources](xos-gui/architecture/data-sources.md)
+    * [Unit Tests](xos/dev/unittest.md)
 * [Testing CORD](cord-tester/README.md)
     * [Running Tests](cord-tester/running.md)
     * [Test Environment](cord-tester/qa_testsetup.md)