Add METADATA to walt: Apache2=NOTICE

Cherry-pick from the master branch to prevent merge conflicts.

Bug: 149721303
Test: N/A
Change-Id: I166eb01a5da30caacf113712b158d5c7dd999d97
Merged-In: I166eb01a5da30caacf113712b158d5c7dd999d97
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
+}