I agree with Brett and Carol here.  This is part of the language syntax.  We can educate people to that effect more if desired (I like the blog post idea).  People will figure it out.

We've already got high ranked stackoverflow answers related to this when you search:
 https://stackoverflow.com/questions/24735311/python-what-does-the-slash-mean-in-help-output/
 https://stackoverflow.com/questions/28243832/what-is-the-meaning-of-a-forward-slash-in-a-python-method-signature-as-show/

Today, we don't document what is positional only, adding this notation is an improvement because it communicates that detail to anyone interested in understanding it without adding a pile of text to all sorts of function signatures.