Hosting Folder in the home directory using nginx

You don't need to add anything to nginx upon user creation. Simply use something like this in your server block:

location ~ ^/~(.+?)(/.*)?$ {
    alias /home/$1/www$2;
    autoindex on;
}

Check your distributions /etc/skel

if you mkdir /etc/skel/www all userdirs created by adduser (or your distributions adduser-script) will have this directory by default.