neo: Complete the documentation of neo.nit.

The documentation of the database model missed many attributes and
relationships. I only added the missing documentation.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>
Si tu veux faire un lien vers `Location.to_s` il faut écrire
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SEE: `Location.to_s` 
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