DOC: update plot_denoise example to use estimate_sigma
DOC: update plot_denoise example to use estimate_sigma

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