Add external/icu/OWNERS.

Test: build/make/tools/checkowners.py -c -v external/icu/OWNERS
Change-Id: Ifb038a018576c814e5f10387e7fed2d7f66ed933
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..94d2383
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,5 @@
+mscherer@google.com
+roubert@google.com
+
+jsauer@google.com
+nfuller@google.com