I assume you are referring to the recent murder of two New York City policemen. The sentence was written on Instagram before the writer committed the murders. The word "pig" is an ugly pejorative term for a policeman. To "put wings on" someone means to kill him. The person who wrote those words meant that he intended to kill two policemen, and was generally advocating killing two policemen each time a black person is killed by a policeman. Ironically, the only pig involved was the disgusting man who wrote those words.

No, it isn't an idiom. We do have a related idiom, though: 'pigs will fly'. We use this to suggest that something is very unlikely to happen. Putting wings on pigs might mean that they are making something happen that is supposedly impossible. Does that make sense in the context of the article?