In the software industry, a high-reputation Stack Overflow profile is seen as a sign of competence, because you have to use the same technical knowledge and research skills required by your job to answer questions there. But in academia, people - at least, the people who make up the majority (though perhaps not the entirety) of tenure and grant review committees, funding agencies, and research directors - tend to see anything that's not actual research as a distraction from research. For that reason participation on this site doesn't play the same role to a professional physicist as participation on Stack Overflow does to a professional developer. Participation in Physics SE is probably best framed as a service activity, like other kinds of community outreach or volunteer work (not that you would put non-physics-related volunteer work on your CV), rather than as a demonstration of your knowledge of physics.
Professors reviewing CVs do look for some amount of service activities, but in many cases they do so only grudgingly, as a concession to the requirements of running a department and/or pressure from university administrators. (And something analogous applies to those in a non-academic environment.) This tends to be somewhat correlated with age, so that e.g. younger professors are a little more likely to look favorably on things like having a blog or contributing to Physics SE. As a graduate student, I don't think it can really hurt you that much to include it, but at later stages of your career (if you go for a career in academia) I think it's important to make it clear that this is not something that consumes a lot of your time, otherwise it probably could hurt your prospects.
As for what exactly to include: I'd put something a little more substantial than what you've quoted. A brief paragraph (2, maybe 3 sentences) that explains what Physics SE is and/or what you do here is probably going to be useful. (I don't have easy access to my own CV at the moment otherwise I'd give you an example, though I doubt that example would be any better than what you'd come up with on your own.) But again, don't play up the amount of time you've invested in the site; better to frame it as something that you use as a resource to improve your education.
I'm sure this has also been pondered extensively on Academia so you could check there for more thoughts, not specific to physics.