The fix in #259 only worked for reports being printed at generation
of the PDF. This PR handles sending an attachment to a printer through
the Print Attachment wizard.
Also clarify the configuration section of the README.
instead of sending a temporary random file name as the title of the job,
use the report file name. Since this is not displayed by default by
cups, document how to configure the CUPS server so that the information
can be displayed.
Clean up the temporary file after printing to avoid cluttering the
server in the long run.
