Warning for data files being needed for releases

**Describe the bug**
Currently there is a warning in the [public data guidance section](https://dfe-analytical-services.github.io/analysts-guide/statistics-production/ees.html#public-data-guidance) saying that releases can't be published without it and there is a warning about missing metadata stopping releases from being published in the [data and files section](https://dfe-analytical-services.github.io/analysts-guide/statistics-production/ees.html#data-and-files). However, there is no explicitly mention of the needing a csv/data file to be uploaded for releases.

**Proposed solution**

- [ ] Can we make this more explicit in the guidance? We can make that warning box include data files
- [ ] Include a guidance section on what teams should do if they don't have a datafile

**To Reproduce**
Steps to reproduce the behavior:

Go to the links above and read the guidance and you'll find the information missing.