Include a disclaimer about using Record Dot Preprocessor in Plutus Validators

[peter-mlabs]

Apparently, you run in E042 (unsupport feature; kind) errors if you use record dot accessors in validator code.

I'm not certain why, but Las pointed this out to me and it fixed the issues I was having. It's the weekend, so I don't expect a deep dive on what is causing this, but he mentioned "it is a feature, i.e. by design".

I think this is worthwhile including, but I'll defer to experts as to whether or not a more in-depth explanation is worth including in the style guide.