::  graph-store|add-signatures: add signatures to a node at a particular uid
::
/-  *graph-store
:-  %say
|=  $:  [now=@da eny=@uvJ =beak]
        [[[=resource =index] =signatures ~] ~]
    ==
:-  %graph-update-3
^-  update
[now [%add-signatures [resource index] signatures]]