Documentation: jlink 21 deprecates some --compress values

[janosvitok]

      --compress <compress>             Compression to use in compressing resources:
                                        Accepted values are:
                                        zip-[0-9], where zip-0 provides no compression,
                                        and zip-9 provides the best compression.
                                        Default is zip-6.
                                        Deprecated values to be removed in a future release:
                                        0:  No compression. Equivalent to zip-0.
                                        1:  Constant String Sharing
                                        2:  Equivalent to zip-6.

Source: https://github.com/openjdk/jdk/commit/784f7b146264ee8eb382f0cc90514018fc5d16d0

TODO:

Mention in documentation that for JDK 21+ '--compress', 'zip-6' instead of '--compress', '2' must be used.