DOCS-3599 Replace 'ubuntu' with 'debian'

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3599 Add Enterprise Debian installation docs

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3599 Add Enterprise Debian installation docs

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-3599 Use 'main' section for Debian packages

Signed-off-by: Sam Kleinman <samk@10gen.com>