Subject: "The file specified to gunzip has not been compressed"

From: 積丹尼 Dan Jacobson <[email-masked]>
Date: Fri, 10 Nov 2017 13:58:46 +0800

man page says
DIAGNOSTICS
       file: not in gzip format
              The file specified to gunzip has not been compressed.

Please add something like:
"...or yes, compressed, but not by gzip or a program gzip is familiar with."