Update examples in README

[heyman]

This PR has the following changes to the README:

• Previously, the examples didn't work because of invalid imports. This PR should fix that. Note that for the interactive notifications, I've only updated the imports and not tested it (I've tested the other functions).
• Add info about calling the init() function.
• Remove info on <YourAppName>.entitlements, since app.entitlements seems to be the only valid filename

[farfromrefug]

@heyman thanks a lot for this!