[docs] add sample commands for test exec

README.md

diff --git a/README.md b/README.md
index fd93be8..b2eab56 100644
--- a/README.md
+++ b/README.md
@@ -15,4 +15,8 @@
 
 For license information, see the file COPYING.
 
+For build information, see the file BUILD.md.
+
+For test execution, see the file TESTING.md.
+
 Documentation: https://harfbuzz.github.io