Add license_note

Comments not preserved during refresh.

Bug: 68860345

Test: m nothing
Change-Id: Idc33b99358ed750471801b313b4106573ea4639e
diff --git a/METADATA b/METADATA
index 3814b8d..9b2a1bc 100644
--- a/METADATA
+++ b/METADATA
@@ -2,5 +2,6 @@
 #     CONSULT THE OWNERS AND opensource-licensing@google.com BEFORE
 #     DEPENDING ON IT IN YOUR PROJECT. ***
 third_party {
+  license_note: "proprietary"
   license_type: BY_EXCEPTION_ONLY
 }