Add a comment, to point at a possible update point

Signed-off-by: Miloslav Trmač <[email protected]>

internal/manifest/oci_index.go

@@ -103,7 +103,7 @@ func addCompressionAnnotations(compressionAlgorithms []compression.Algorithm, an
 	}
 	for _, algo := range compressionAlgorithms {
 		switch algo.Name() {
-		case compression.ZstdAlgorithmName, compression.ZstdChunkedAlgorithmName:
+		case compression.ZstdAlgorithmName, compression.ZstdChunkedAlgorithmName: // Should this use InternalUnstableUndocumentedMIMEQuestionMark() ?
 			(*annotationsMap)[OCI1InstanceAnnotationCompressionZSTD] = OCI1InstanceAnnotationCompressionZSTDValue
 		default:
 			continue