docs(usage): add docs for TBindingBehavior
docs(usage): add docs for TBindingBehavior

adds usage documentation for the TBindingBehavior

fixes issue https://github.com/aurelia/i18n/issues/39

aurelia/i18n,milunka/aurelia-i18next,milunka/aurelia-i18next,aurelia/i18n,aurelia/i18n