doc: bmaptool can handle compressed wic files

[vermaete]

It is not longer needed to decompress the wic file to be used with bmaptool.

From the man page fo bmaptool:

IMAGE may be compressed, in which case bmaptool decompresses it on-the-fly. The compression type is detected by the file extension and the following extensions are supported:

  1. ".gz", ".gzip", ".tar.gz" and ".tgz" for files and tar archives compressed with "gzip" program
  2. ".bz2", "tar.bz2", ".tbz2", ".tbz", and ".tb2" for files and tar archives compressed with "bzip2" program 3. ".xz", ".tar.xz", ".txz" for files and tar archives compressed with "xz" program 4. ".lzo", "tar.lzo", ".tzo" for files and tar archives compressed with "lzo" program 5. ".lz4", "tar.lz4", ".tlz4" for files and tar archives compressed with "lz4" program 6. ".zst", "tar.zst", ".tzst" for files and tar archives compressed with "zstd" program