Is there any consensus whether you use should a textwidth of 70 or 80
or any other value when writing text documents such as README,

Using 80 is pretty standard. I use it for code, READMEs, etc.
However I do push it back to 65 or 70 for emails, just because if
folks start quoting the email, extra layers of quote-markers
start making things wider.


autofmt : text formatting plugin

:set runtimepath+='~/.vim/autoload/autofmt/'
:set formatexpr=autofmt#japanese#formatexpr()