Signup doesn't work when hCaptcha enabled and keys not configured

I made a pull request to add some more guidance on the site settings to help others avoid this situation. Edit: merged.

Also noticed that there is a warning that should have been displayed on your admin home page to let you know there is a problem with your hCaptcha config. I guess it was not prominent enough?

There is a problem with your hCaptcha site_key or secret_key configuration