add `npm login` to README
add `npm login` to README

dmarcos/aframe,mkungla/aframe,dmarcos/aframe,msimpson/aframe,weddingdj/aframe,mkungla/aframe,darkwing/aframe,wizgrav/aframe,cemkod/aframe,googlecreativelab/aframe,darkwing/aframe,fernandojsg/aframe,cemkod/aframe,chenzlabs/aframe,MatthewShotton/aframe,msimpson/aframe,weddingdj/aframe,chenzlabs/aframe,MatthewShotton/aframe,jaxmolina/ar,RSpace/aframe,aframevr/aframe,googlecreativelab/aframe,jaxmolina/ar,jzitelli/aframe,wizgrav/aframe,fernandojsg/aframe,aframevr/aframe,ngokevin/aframe,RSpace/aframe,jzitelli/aframe,ngokevin/aframe