Hot tip about custom variables

[aerni]

I've run into a complex variable collision issue in Antlers with variables and nested partials. I've talked to @JohnathonKoster about it and there appears to be no real solution to the problem other than prefixing custom variables.

It would be great if the docs on creating variables had one of those hot tips about prefixing custom variables as a best practice. Or maybe even prefixing all custom variables in the docs examples as well.