I\'m working with Yarn v0.16.1. If I understand correctly (according to the documentation), yarn global add should be the equivalent of np
AndrewD gave a great answer, but for those on Windows it's a bit different, especially step 3.
Please do not use the command setx as @Thapedict said.
It will remove all your previous paths you had and replace it with only the given directory.
If you want to use setx, I think there might be a flag to make it append the existing path variables, but I don't know which one. Using only setx will not append to it.
I would just do System Properties > Advanced > Environment Variables > Edit Path > New > c:\users\YOURUSERNAME\appdata\local\yarn\bin
to make sure you don't remove your previous variables.