Clarify EntityPrototype.emissions_per_second

[curiosity]

Right now it says:

Amount of emissions created (positive number) or cleaned (negative number) every second by the entity. This is passive, and it is independent concept of the emissions of machines, these are created actively depending on the power consumption. Currently used just for trees.

The word "these" makes it ambiguous whether it talks about machine emissions or, confusingly, about the ones from this property. It should use the word "which", or better yet link to BaseEnergySource.emissions_per_minute instead, where the specifics of machine emissions should be described.