Added chapter title formatting for numpy_images.rst
Added chapter title formatting for numpy_images.rst

vighneshbirodkar/scikit-image,paalge/scikit-image,rjeli/scikit-image,paalge/scikit-image,vighneshbirodkar/scikit-image,paalge/scikit-image,ofgulban/scikit-image,rjeli/scikit-image,vighneshbirodkar/scikit-image,ofgulban/scikit-image,ofgulban/scikit-image,rjeli/scikit-image