Document option for breaking out data files

[mattstratton]

The site now supports (optionally) moving the program, sponsorship, and organizers sections into separate data files.

As illustrated in the data file directory for 2023-Chicago, it is (optionally) possible to break out either/both the program and sponsors sections of the main.yml into program.yml and sponsors.yml.

Note that organizers.yml is also supported, just not illustrated in 2023-chicago.

[toshywoshy]

While thinking about changes to enhance automation, I am thinking of also moving the organisers out to a different file.
This will make it possible to automate emails to core and the local team when changes come in through a PR.
If slack and/or the mailinglist have an API, we can even do some verification using github actions or some other hooks to make it easier.

[mattstratton]

Organizers already works as a separate file, it’s just not been done with any city yet.