README: document cron fields in example

[thaJeztah]

Because I always have to look up the fields, so may as well document it in the example 😅

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Confirm the readme has been updated if necessary.

[cbraynor]

Thank you for suggesting this - crontab fields are sometimes 0-based and sometimes 1-based and it can be difficult to remember which are which. I made the slight adjustment of matching the current Actions documentation for consistency.

[thaJeztah]

Thanks! Wondering; I originally came to this repo, looking for the template that's used when you add this action to your repository; is that in a public repository, or somewhere private?

[cbraynor]

The specific template is somewhere private as it changes based on a few factors - e.g. languages detected, names of branches, etc. but is very much based off the one in the README. Does the one in this repo meet your needs or are you e.g. looking to suggest these changes there too?

[thaJeztah]

Yes, my initial intent was to include this hint in the template 😅
But no problem; just wanted to check if I looked in the right place 👍