Add Example for POSTing UIImages

RestKit allows you to post images with:

```
RKParams* params = [RKParams params];
RKParamsAttachment* attachment = [params setData:UIImageJPEGRepresentation([thumbnail.image fixOrientation], 0.1) MIMEType:@"image/jpeg" forParam:@"timeline[photo]"];
[[RKClient sharedClient] post:urlString params:params delegate:self];
```

Is there any easy way to do that with LRResty?
