Updates article about Using TWAs (#7201)
Updates article about Using TWAs (#7201)

* Updates article about Using TWAs

- Due to the inclusion of the TwaLauncherActivity that removes the
  need for the developer to author code for TWAs, updated most
  of the Getting Started section.
- Also expanded the article to cater for developers will less
  Android experience.

* Removing d.g.c so that build works

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