Added --disable-ipv6 configure option to server build instructions.
Added --disable-ipv6 configure option to server build instructions.

tltneon/freeciv-web,sylvain121/freeciv-web-server,sylvain121/freeciv-web-server,tltneon/freeciv-web,adaxi/freeciv-web,adaxi/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,andreasrosdal/freeciv-web,andreasrosdal/freeciv-web,adaxi/freeciv-web,tltneon/freeciv-web,andreasrosdal/freeciv-web,adaxi/freeciv-web,andreasrosdal/freeciv-web,tltneon/freeciv-web,tltneon/freeciv-web,sylvain121/freeciv-web-server,andreasrosdal/freeciv-web