How do i gain weight from running?

Ok so i am joining a summer running club. We are going to be running like 5 miles a day, 3 days a week. I'm already in pretty good shape, I want to know how i can use this running to get muscular and not turn into one of those kids with no muscle just bones. If you've ever seen good runners they almost always look like human skeletons. How do i avoid turning into a human skeleton? I want to use all this running to get big/muscular not to get really skinny.