update schedule

[pbellec]

we may want to have a drop-down menu with different dates

[pbellec]

we'll do this later, but in the meantime we can add a disclaimer that this is the old schedule from 2023, provided for information, and that updated schedule will be released soon.

[pbellec]

There are now individual schedules listed for each site. It's suggested to link to a gcal or a an external doc, so each site can easily maintain and update their schedule without changing the website itself.