Add scope to package.json to make NPM happy. Doc fix.

[thevictorlopez]

NPM complains about the xarf name:

npm notice Publishing to https://registry.npmjs.org/ with tag latest and default access
npm error code E403
npm error 403 403 Forbidden - PUT https://registry.npmjs.org/xarf - Package name too similar to existing packages xhr,xhr2,raf,vary,arg,tar,yarn; try renaming your package to '@xarf/xarf' and publishing with 'npm publish --access=public' instead
``` 

Adding the `@xarf` scope to address this.