Some docstrings for replace_node (#3244)
Some docstrings for replace_node (#3244)

* Some comments for replace_node

* Update src/ngraph/graph_util.hpp

@csullivan done figured it out

Co-Authored-By: Chris Sullivan <5c890bf96df53a6471c186dae20a2dc269aee7cc@intel.com>

* Update graph_util.hpp

NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph,NervanaSystems/ngraph