message: Add operator+= to StorableResources
diff: @@ -19,6 +19,12 @@ struct StorableResources
  return out;
  }
  + StorableResources& operator+=(const StorableResources& other)
  + {
  + *this = *this + other;
  + return *this;
  + }
  +
  StorableResources operator-(const StorableResources& other) const
  {
  StorableResources out;
  