Add parameter to exclude usernames

generate.py

@@ -37,6 +37,7 @@ if __name__ == "__main__":
     parser.add_argument("-s", "--size", type=int, help="Ticket height, defaults to 150.", default=150)
     parser.add_argument("-m", "--margin", type=int, help="Margin (depends on printer), defaults to 0.", default=0)
     parser.add_argument("-g", "--gap", type=int, help="Gap between tickets, defaults to 0.", default=0)
+    parser.add_argument("--exclude-usernames-from", action="append", help="File with usernames that should not be used.", default=[])
 
     args = parser.parse_args()
 
@@ -63,7 +64,12 @@ if __name__ == "__main__":
 
     pdf = canvas.Canvas(args.output, pagesize=A4)
     page_width, page_height = A4
+
     used_usernames = set()
+    for exclude_usernames_file in args.exclude_usernames_from:
+        with open(exclude_usernames_file, 'r') as file:
+            for line in file:
+                used_usernames.add(line.strip())
 
     ticket_height = args.size
     qr_code_size = ticket_height/1.5