Getting Started Cleanup

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 facebook#7477

Reviewed By: vjeux

Differential Revision: D3281639

Pulled By: JoelMarcey

fbshipit-source-id: ca956d97293ac3793431cb54f3560ee3e52c0dce

[0.26.0-rc] Bump version numbers

[0.25.1] Bump version numbers

[0.25.0] Bump version numbers

[0.24.1] Bump version numbers

[0.24.0] Bump version numbers

[0.25.0-rc] Bump version numbers

[0.24.0-rc5] Bump version numbers

[0.24.0-rc4] Bump version numbers

[0.24.0-rc3] Bump version numbers