package.json should include engines property to note dependency on node 12

[ghost]

I was currently on node 10 and trying to use the latest version, which doesn't work due to no native Promise support. The package.json should note that node 12 is a dependency via the engines property so npm installs on node 10 will throw a warning.

[TrySound]

@lambertsteven You can always polyfill promises with es6-promise. I wouldn't like to get the warning everytime I install this on old machine.

[ghost]

I can understand that. Could we get a note on the readme at the least that postcss-import depends on native Promises and either that requires node 12 or es6-promises?

[TrySound]

@lambertsteven It make sense for postcss readme, cause postcss-import and all postcss plugins depends on it.
But https://github.com/postcss/postcss#usage