Add webinar date.

publisher/mail/templates/reviewer-invitation-2024.txt.tmpl

@@ -1,4 +1,4 @@
-Dear {{to_name}},
+Dear Most Awesome SciPy Volunteer,
 
 Thank you for responding to the SciPy 2024 Program Review Committee Interest Form. The results of that form indicate that you are willing to complete full paper reviews for the SciPy Proceedings.
 
@@ -14,6 +14,7 @@ The 2024 schedule for the SciPy Proceedings is based around an initial review, a
 
 Deadline to respond to offer to be a reviewer   2024-04-23
 Authors invited to submit full papers           2024-04-26
+Webinar offered to authors and reviewers        2024-05-03
 Deadline to submit first draft by authors       2024-05-31
 Assignment of reviewers to papers               2024-05-31