Add OWNERS in hardware/broadcom/libbt

* 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: I8cefacce7c1f71a39c13547c47c1369017d4c940
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..54afe3b
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,4 @@
+eisenbach@google.com
+mylesgw@google.com
+pavlin@google.com
+siyuanh@google.com