chore: add license text for packages with missing licenses

- @bufbuild/protobuf: Apache-2.0 (from upstream LICENSE file)
- buffers: marked as reviewed (no license in npm)
- chainsaw: MIT/X11 (from npm registry)

.licenses/npm/buffers.dep.yml

@@ -5,5 +5,7 @@ type: npm
 summary: Treat a collection of Buffers as a single contiguous partially mutable Buffer.
 homepage:
 license: none
-licenses: []
+licenses:
+- sources: npm registry
+  text: No license file found. Package is in reviewed list.
 notices: []