Bug 27085: Corrections in overdue_notices.pl help text

Bug 27085: Corrections in overdue_notices.pl help text

-library      <branchname>     only deal with overdues from this library (repeatable : several libraries can be given)
Should be <branchcode>

Help text should also be proper sentences.

To test:
0) Run misc/cronjobs/overdue_notices.pl -h
1) Check that the text is now:
   -library      <branchcode>     Only deal with overdues from this library.
2) Check that the rest of the help text are proper sentences,
   with leading capital letter and punctuation.
3) Sign off.

Sponsored-by: Lunds Universitetsbibliotek
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>