THRIFT-2946 Enhance usability of cross test framework

introduce *make fail* to update known failures
diff --git a/test/README.md b/test/README.md
index ef874ac..91e4c26 100755
--- a/test/README.md
+++ b/test/README.md
@@ -101,6 +101,10 @@
     test/test.py --skip-known-failures
     test/test.py --update-expected-failures=merge
 
+to update the known failures, run
+
+    make fail
+
 ## Test executable specification
 
 ### Command line parameters