Add oidc-preferences library imports to README

[availe]

Minor update to documentation.

[kalinjul]

Did you need the dependency at any point?
It should not be required when using the CodeAuthFlowFactories.

I think the problem is rather that i didn't mark it as an api dependency for appsupport, which it propably should be..

[availe]

I created my own CodeAuthFlowFactory, since I wanted web app to use a redirect instead of a popup. Safari goes out of its way to hide browser popups, which was... problematic for a login page.

But marking preferences as an api would probably also help.