Merge pull request #2 from villander/doc/usage

Improve usage linking externalRoutes as API

Author: villander

README.md

@@ -24,7 +24,7 @@ ember install ember-engines-router-service
 
 ## Usage
 
-Basically you have all [RouterService](https://api.emberjs.com/ember/release/classes/RouterService) API **inside each engine** such as `transitionTo` and `isActive` and also the same one using new "external routing" APIs such as `transitionToExternal` and `isActiveExternal` to link external routes.
+Basically you have all [RouterService](https://api.emberjs.com/ember/release/classes/RouterService) API **inside each engine** such as `transitionTo` and `isActive` and also the same one using new "external routing" APIs such as `transitionToExternal` and `isActiveExternal` to link `externalRoutes`.
 
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 ```js