[Docs] Add onboarding documentation to Wiki

[gino-m]

Some things to include:

• Required tutorials:
  • Android development with Android Studio
  • RxJava tutorial / videos
  • Basic dependency injection with Dagger 2
  • Git and Github tutorials
  • Reactive MVVM architecture
  • JUnit, Espresso
• Optional intro tutorials:
  • Intro to Android databinding
  • Cloud Firestore
  • Room ORM
  • Maps API for Android
• Links to other relevant Wiki docs

Also, consolidate links:

• Project overview
• Design/architecture
• Best practices

[gino-m]

@scolsen FYI

[scolsen]

Related #102