In order to add source to the origin at the bottom of each of your feedwordpress posts, you need to install additional plugin found here.
After installing the plugin, activate it.
Now simply go to your feedwordpress settings under Posts and Links.
Scroll all the way down where you see "Attribution Boilerplate"
Click Add new boilerplate
specify to add before or after the content.
in the text box type something like <a href="[original url]"> Source article</a>
you are now good to go.