DocumentRoot is /usr/local/var/www.
The default ports have been set in /usr/local/etc/httpd/httpd.conf to 8080 and in
/usr/local/etc/httpd/extra/httpd-ssl.conf to 8443 so that httpd can run without sudo.
To have launchd start httpd now and restart at login:
brew services start httpd
Or, if you don't want/need a background service you can just run:
Running apachectl -X appears to run Apache in the foreground so I can hit Ctrl+C to quit it again, using the config file at /usr/local/etc/httpd/httpd.conf and serving the index.html file from /usr/local/var/www (which confusingly says "Welcome to nginx", presumably because I installed nginx via Homebrew earlier).