I tend to go for (simple) markdown rather than pure text files. It can be rendered into some fancy format, but the source code is also readable to humans. With chat apps like Slack and Discord taking it up, even non-technical people tend to understand what it means to put emphasis on something. You get the benefits of plain text with the ability to empathise, without fancy formats. Such a format also enforces paragraphs and lists to be consistent, which is great for easy of reading.

There are other, similar slightly-more-than-plain-text formats (RST is common among some communities, for example) with the same benefits, and everyone can pick their favourites and use them freely because in the end these formats are easy to parse as a human.