message: docs: add info regarding injecting custom pipes
  Indicate that a pipe also needs to be included in the providers array
  PR Close
diff: @@ -212,7 +212,8 @@ Now you need a component to demonstrate the pipe.
  Note the following:
  * You use your custom pipe the same way you use built-in pipes.
  -* You must include your pipe in the `declarations` array of the `AppModule`.
  +* You must include your pipe in the `declarations` array of the `AppModule`
  +* If you choose to inject your pipe into a class, you must provide it in the `providers` array of your `NgModule`.
  <div class="callout is-helpful">
  