Update Doc/Readme

[adamtarmstrong]

TouchID never needed a plist key setting, but it appears to use FaceID, this is required. Docs should be updated to state that users need to add this to the iOS plist:

<key>NSFaceIDUsageDescription</key> <string>any usage description</string>

[raybelisle]

Documentation needs to be updated to include:

• createKeychainItem in Identity, this method is not documented.
• keychainItem is defined as a Dictionary type, but documentation does not define dictionary items.