Add OWNERS to external/google-benchmark

Bug: 33166666
Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: Ieaa39beb820ea84a8db6f4b68e944cd9f324896e
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..eb1a375
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,2 @@
+maco@google.com
+dominic@google.com