Bug 35596: Error in writeoff_debts documentation

Bug 35596: Error in writeoff_debts documentation

This patch corrects an error in the documentation of the
writeoff_debts.pl script. The --type parameter accepts debit type codes,
not credit type codes.

To test:
-  Run ./misc/cronjobs/writeoff_debts.pl
-  Make sure the sentence for --type makes sense, grammar and spelling
   are correct

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit 633533049ad234f8705390e4b6c78987e90b2802)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit 97cc3285bd0ce18541d0fbeef4e6996e33c395eb)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>