add js extensions to readme
add js extensions to readme

systemjs/builder,systemjs/builder,systemjs/builder,alexisvincent/builder,lookfirst/builder,lookfirst/builder,matthewbauer/builder,richardTowers/builder,tonytanger/builder,JeroenVinke/builder,douglasduteil/builder,robwormald/builder,alexisvincent/builder,synaptek/builder,ahmedshuhel/builder,Psvensso/builder,Munter/builder,buddhike/builder,jrauschenbusch/builder,Psvensso/builder,matthewbauer/builder,jrauschenbusch/builder,whitneyit/builder,whitneyit/builder,buddhike/builder,richardTowers/builder,robwormald/builder,jrauschenbusch/builder,JeroenVinke/builder,Munter/builder,tonytanger/builder,douglasduteil/builder,synaptek/builder,alexisvincent/builder,ahmedshuhel/builder,alexandr2110pro/builder,alexandr2110pro/builder