Add Flickr-specific sample code to the README

[deg]

This PR is in response to #28

I'm not completely happy with it but, realistically, I'm not going to have time to do much better anytime soon. Even as is, this does contain helpful info for anyone trying to work with Flickr. But, I'll completely understand if you want to move this into a separate file rather than leaving it in your main README.org.

Problems:

• This is not fully tested. The code is cut-n-pasted from my working app, but I have not tested in isolation. I was careful, but may have missed some bits.
• The flow is different than in your Twitter sample. This is from the server side of a Compojure-based client/server app.

That said, there is value here. I struggled for a while before I figured out how to get oauth-clj to work in my app and with Flickr. This captures what I learned and will, I hope, be useful for the next person who tries.

[r0man]

@deg What about adding this to the Wiki instead of the README?

[deg]

That would be fine.