Bug#1029587: Add simplest example

[Dan Jacobson]

Package: p7zip-full
Version: 16.02+dfsg-8
Severity: minor
File: /usr/share/man/man1/7z.1.gz
X-Debbugs-No-Ack: noack

On the 7z man page add an additional most simplest example of
7zipping and unzipping a single file. Thanks.

$ 7z a d.7z d

perhaps.