Générer un PDF avec DITA Open Toolkit sous GNU/Linux: install dita-ot via aptitude

- replace Dita Open Toolkit manual installation by installation via aptitude
- change text accordingly

Signed-off-by: Olivier Carrère <carrereo@gmail.com>
Acked-by: Angela Cristina <acristina@redaction-technique.org>
Fix XML code

- add Debian Linux path to DTDs
- fix missing double quotes
- fix missing closing tags
- fix indentation

Signed-off-by: Olivier Carrère <carrereo@gmail.com>
Acked-by: Angela Cristina <acristina@redaction-technique.org>