title: Angular 8 Firestore accessing all values in a subcollection
body: <p>Im a little confused on Firestore structuring.</p>
  
  <p>If I have a collection 'Users'/ + uid,(I'm using the user id for firebase authentication for the document id), then I have a subcollection under that named flashCards.</p>
  
  <p>How would I access the properties of that subcollection to using ngfor to show them all on the screen?</p>