Add examples README.md

Related to https://github.com/request/request/issues/1202 - I decided not to write tests, because the examples I just added would require apps, credentials, and storing refresh tokens as well.

The first two examples are just for refreshing tokens, the OAuth1.0 one I'm using only for Yahoo ATM, the OAuth2 one seems much more widely adopted.

About the Flickr example, there are modules out there just to solve that problem, so I though it would be useful to share it.

Also I have no idea if that was the point with the examples, so feel free to scratch it out :grinning: