Add documentation for subdomain behavior

This reverts commit 3f601b0

README.md

@@ -317,6 +317,10 @@ Puma-dev supports domains, not just TLDs. `puma-dev -install -d test:puma.dev` w
 
 Like pow, puma-dev support serving static files. If an app has a `public` directory, then any urls that match files within that directory are served. The static files have priority over the app.
 
+### Subdomains support
+
+Once a virtual host is installed, it's also automatically accessible from all subdomains of the named host. For example, a `myapp` virtual host could also be accessed at `http://www.myapp.test/` and `http://assets.www.myapp.test/`. You can override this behavior to, say, point `www.myapp.test` to a different application: just create another virtual host symlink named `www.myapp` for the application you want.
+
 ### Status API
 
 Puma-dev is starting to evolve a status API that can be used to introspect it and the apps. To access it, send a request with the `Host: puma-dev` and the path `/status`, for example: `curl -H "Host: puma-dev" localhost/status`.