Add notes about passing secrets via environment variables

[potiuk]

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[Lee-W]

Mostly looks good to me. Just thinking whether we should use warning 🤔

[potiuk]

Just thinking whether we should use warning

Warnings are when you are doing somethign and you should be careful, I think it's just "common sense" to not pass secrets this way - just stating it explicitly as separate chapter is probably a bit more powerful - like just a "normal" thing :D.

Warnings are - in a way - a bit less visible, when you want to find "how do I do something" - separate chapters are likely more discoverable, and I'd usually use them to drag attention to certain un-obvious aspect of something that you want to read about - in this case it's just plainly stating "don't do it".

[Lee-W]

sounds good 🙂