message: Update doc to split summary and description
diff: @@ -20,9 +20,8 @@ op {
  "A `Tensor` of type T. An alias of `x`. The content "
  "of `y` is undefined if there are duplicates in `i`."
  }
  - summary: <<END
  - Adds v into specified rows of x.
  -
  + summary: "Adds v into specified rows of x."
  + description: <<END
  Computes y = x; y[i, :] += v; return y.
  END
  }
  