Summary:
1. Remove note about upgrading Homebrew packages. That was kind of noisy.
2. Use local images instead of those stored on Akamai.
3. Add wording for modifying test project about actually opening a file.
4. Add note about keeping initial defaults for Android Studio install in tact.
Tested site locally. Images and new wording appeared as expected.
Closes https://github.com/facebook/react-native/pull/7477
Reviewed By: vjeux
Differential Revision: D3281639
Pulled By: JoelMarcey
fbshipit-source-id: ca956d97293ac3793431cb54f3560ee3e52c0dce