README.md: add default_url to example README
README.md: add default_url to example README

default_url is only used by IRC bot but prints undefined if it isn't
specified.

TODO: check options array for required options

ebensing/dreadnot,racker/dreadnot,pipedrive/dreadnot,fr34k8/dreadnot,pipedrive/dreadnot,ebensing/dreadnot,racker/dreadnot,ebensing/dreadnot,pipedrive/dreadnot,racker/dreadnot,fr34k8/dreadnot