Added step by step instructions for use.

I used this module to back up my own Flickr account and I had a lot of
issues struggling with the auth_token and frob stuff, so when I figured
it out I thought I'd better document it.

Included is a script for fetching the authorization URL for your app. I
called it net-flickr-backup-get-auth-token to avoid coliding with other
binaries installed on the system.

Finally, I renamed backup.pl to net-flickr-backup-do-backup for the same
reason mentioned above, and for consistency.
Makefile should not be stored in version control.
Added three dependencies to the Build.PL

Digest::MD5, URI, and Config::Simple are all used by the new
net-flickr-backup-get-auth-token binary.
Added to the POD a note about submitting patches.

Flickr can change their stuff all the time, and I've not tested these
instructions since I used them in May 2012 so they could already be out
of date. Hopefully the next person will update them if necessary.
Added a test to check that the binaries compile.