Add OWNERS in system/nvram

Owners are selected from top CL approvals or owners.
They will be suggested to review/approve future CLs.

Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: Ib96f30b6779b6dcb57cab15bd8cb5675baf1b9cf
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..b3680ec
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,2 @@
+dkrahn@google.com
+mnissler@google.com