mustard and collard greens recipe

Ingredients: 1 bunch collard greens, stems removed and leaves chopped 1 bunch mustard greens, stems removed and leaves chopped 2 tablespoons olive oil 1 onion, finely chopped 3 cloves garlic, minced 1 smoked ham hock or 4 slices of bacon, chopped 4 cups chicken broth (or vegetable broth for a vegetarian option) 1 teaspoon red pepper flakes (optional for some heat) Salt and pepper, to taste 2 tablespoons apple cider vinegar