Minor update documentation of facet_components().

Former-commit-id: 4776cc55764167c0831dc1b6a0b0fa3b403b5417

include/igl/facet_components.h

@@ -27,6 +27,7 @@ namespace igl
   //   triangle_triangle_adjacency.h)
   // Ouputs:
   //   C  #F list of connected component ids
+  //   counts #C list of number of facets in each components
   template <
     typename TTIndex, 
     typename DerivedC,