Add punctuation conventions to techniques

[mattgarrish]

I can't find mention of punctuating the output in the guidelines or techniques. I know we're intentionally leaving this so people can localize the strings easier and change it depending on whether they want to list or concatenate values, but we shouldn't leave this rationale unsaid.

I'd add a brief subsection to the implementation conventions to explain this is left to developers to code as they see fit.