Update README: can now use modifiers
Update README: can now use modifiers

Using modifiers from `mobx-angular` is supported since v3.1.0.
mobxjs/mobx-angular,500tech/ng2-mobx,mobxjs/mobx-angular,mobxjs/mobx-angular,500tech/ng2-mobx,mobxjs/mobx-angular,500tech/ng2-mobx