Add METADATA to spirv-headers: MIT=NOTICE am: 2cb335583c am: b8530f4af8 am: 36d9c93da9 am: bdd05e9c9f

Change-Id: I1984b59ff494f12cc3c943aa62d4828f0ee07d33
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..d97975c
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,3 @@
+third_party {
+  license_type: NOTICE
+}