Add OWNERS in external/libhevc

* Owners are selected from top CL approvals or owners.
  They will be suggested to review/approve future CLs.
* OWNERS files are recognized by the new find-owners plugin, see .md files in
  https://gerrit.googlesource.com/plugins/find-owners/+/master/src/main/resources/Documentation/

Test: build/make/tools/checkowners.py -c -v OWNERS
Change-Id: Ic53b6d2f7108f983ea8acdeab4a9496288a2ef5a
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..4516783
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,2 @@
+marcone@google.com
+essick@google.com