message: docs: reword explanation for using singleton services decorative to be more understandable
  To understand the current sentence it requires to read it multiple times.
  This fix should help developers to understand the sentence in a quicker way.
  PR Close
diff: @@ -9,7 +9,7 @@ For a sample app using the app-wide singleton service that this page describes,
  There are two ways to make a service a singleton in Angular:
  -* Declare `root` for the value of the `@Injectable()` `providedIn` property
  +* Set the `providedIn` property of the `@Injectable()` to `"root"`.
  * Include the service in the `AppModule` or in a module that is only imported by the `AppModule`
  