Bug 6680 - simple tidy-up of cart download format descriptions

Bug 6680 - simple tidy-up of cart download format descriptions

Explains what uses RIS, and replaces iso2709 with 'MARC'.

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Ian Walls <ian.walls@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Simple change, all tests pass.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>