Add context to package.json file for custom auth flow (iOS & Flutter)

[Kilo-Loco]

Friction Log Item: https://app.asana.com/0/1201897617263927/1202313698670627/f

Description of changes: Adds more context to the contents of package.json which is a file & concept that wouldn't be immediately apparent to some iOS and Flutter developers.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.