Add OWNERS for SignApk

Test: build/make/tools/checkowners.py -c -v OWNERS
Bug: 30972906
Change-Id: I7a2c9301376e24239924ffbedcb2b97727da700a
diff --git a/tools/signapk/OWNERS b/tools/signapk/OWNERS
new file mode 100644
index 0000000..0b8d398
--- /dev/null
+++ b/tools/signapk/OWNERS
@@ -0,0 +1,2 @@
+cbrubaker@google.com
+klyubin@google.com