doc(readme): clarify the description of this library
doc(readme): clarify the description of this library

Fixes https://github.com/aurelia/validatejs/issues/103

ericIMT/validation,manuel-guilbault/aurelia-validation,aurelia/validation,aurelia/validation,JeroenVinke/validation,manuel-guilbault/aurelia-validation,ericIMT/validation,JeroenVinke/validation