Add description: decode-marc21 needs UTF-8 encoding

See metafacture/metafacture-documentation#23.

Author: dr0i

metafacture-biblio/src/main/java/org/metafacture/biblio/marc21/Marc21Decoder.java

@@ -135,7 +135,7 @@
  */
 @In(String.class)
 @Out(StreamReceiver.class)
-@Description("Decodes MARC 21 records")
+@Description("Decodes MARC 21 records (UTF-8 encoding expected).")
 @FluxCommand("decode-marc21")
 public final class Marc21Decoder extends DefaultObjectPipe<String, StreamReceiver> {