Make it clear that CSV exports are limited

This is addressed in a PR I just opened: https://github.com/farmOS/farmOS/pull/783

It doesn't add much, just a warning to users that CSV exports do not contain all data.

I considered adding more, like suggesting using the API to get access to all data, but I decided against it. A farmOS instance may offer users access to CSV exports without offering them access to the API, so it could be confusing/misleading/undesirable to make suggestions that are impossible in specific instances.

I think the simple warning serves the original purpose, to "make it clear that CSV exports are limited."

Closing this under the assumption that the PR will be merged...

Automatically closed - issue fixed for 2 weeks with no activity.