Update doc - Need to include 'formData' as key instead of 'params'

I have been working with these directives on these days and I realised that it wasn't sending any data from 'params' (just the file datas) until I found looking into the jquery plugin that the key for uploading all the information was 'formData'. After that change everything works as expected :)
Merge pull request #4 from rosUnix/patch-1

Update doc - Need to include 'formData' as key instead of 'params'