docs/system/s390x: Improve the 3270 documentation

There is some additional information about the 3270 support in our Wiki
at https://wiki.qemu.org/Features/3270 - so let's include this information
into the main documentation now to have one single source of information
(the Wiki page could later be removed).

While at it, I also shortened the lines of the first example a little bit.
Otherwise they showed up with a horizontal scrollbar in my Firefox browser.

Message-Id: <20200713075112.442-1-thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

0 files changed, 0 insertions, 0 deletions