Add gtest-parallel to open-source projects.

README.md

@@ -73,6 +73,9 @@ listener for Google Test that implements the
 [TAP protocol](https://en.wikipedia.org/wiki/Test_Anything_Protocol) for test
 result output. If your test runner understands TAP, you may find it useful.
 
+[gtest-parallel](https://github.com/google/gtest-parallel) is a test runner that
+runs tests from your binary in parallel to provide significant speed-up.
+
 ## Requirements ##
 
 Google Test is designed to have fairly minimal requirements to build