Add support for authenticated Jenkins builds

This is a great utility, thanks for the hard work! Sadly I was unable to find it when doing a bit of a search for Jenkins build status indicators. Instead a Pivot pointed it out to me :kissing_heart: :gift_heart:

Anyway I decided to quickly add support for polling Jenkins builds that require OAuth:

- Added 2 optional arguments to Jenkins check script
- Documented 2 new arguments in README.md