web: add payment information to spam

web/webapp/templates/mailing/due.txt

@@ -23,6 +23,13 @@ Here's detailed information about your recent transfers:
   '%.02f'|format(t.transfer.amount/100) }} PLN transfer on {{ t.transfer.date.strftime('%Y-%m-%d') }}
 {%- endfor %}
 
+Here's our wire transfer information:
+ - STOWARZYSZENIE WARSZAWSKI HACKERSPACE
+ - 48 1950 0001 2006 0006 4889 0002
+ - {{ member.username }} - {{ member.type }} - składka
+
+For more information, see https://wiki.hackerspace.pl/finanse
+
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