Bug 10703: Document borrower_files table

Bug 10703: Document borrower_files table

Add db documentation to borrower_files table.

To test:

apply
review kohastructure.sql to be sure documentation is there

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Comment: No errors. Tested loading on new database.
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 09e802c7933073cd98040155b02898ab79739b3a)
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>