There's many many frameworks out there that each have their own way of dealing with a standard Servlet. I think it's best to presume that a user knows how this would work in their favourite framework, so there's no need to clutter the docs with multiple fragments of solutions.

If you want to share this information, I'd suggest a blog post or similar that can go into more depth than reference documentation like this.

The MetricsServlet is not a singleton, you can have as many of them as you like (though usually only one).

Another quick way to share your info would be to post a question on StackOverflow that you answer yourself.