[compression_utils] Document existence of atool

compression_utils/README

@@ -3,9 +3,20 @@
 The lz.sh script emulates and extends commands lz and uz from the
 mtools.
 
-It handles: tar, tar.gz, tar.bz2, tar.xz, tar.lzma and tar.Z (and
+NOTE: although more powerful than their mtools equivalent, you should
-associated 3-characters extensions: tgz, tbz, tb2, tlz, txz, taz)
+probably use als and aunpack from the atool package rather than these
-through the standards options of GNU Tar.
+commands; they are much better and there are several other useful
+commands provided by atool. This script is still useful when you can't
+install Perl (atool ist written in Perl).
+
+This script handles the following archive formats through the standards
+options of GNU Tar:
+- tar
+- tar.gz (tgz)
+- tar.bz2 (tbz, tb2)
+- tar.xz (txz)
+- tar.lzma (tlz)
+- tar.Z (taz)
 Note that you need GNU Tar, at least version 1.20 to support LZMA
 compressed archives, and version 1.22 for XZ compressed ones.
 
@@ -35,3 +46,8 @@ In case of recompression, the original compressed file is kept. In
 case of compression (i.e. when the suffix of the file does not
 correspond to a known compression format), the original uncompressed
 file is removed.
+
+NOTE: the atool package provides the arepack command, which can
+recompress to several formats and not only to xz. xzize has the
+advantage to recompress on the fly rather than unpacking the archive
+entirely on the file system and repacking it after.