Update readme based on the internal redesign

[frederikprijck]

Description

Restructures the readme file based on our internal design to try and create a uniform experience across the readme's of our different SDKs.

• [ ] Add header image

Checklist

• [x] I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• [x] All active GitHub checks for tests, formatting, and security are passing
• [x] The correct base branch is being used, if not the default branch

[stevehobbsdev]

Looks good. The API reference methods aren't explicitly called out like they are in the Figma example, are we leaving this out?

See the Figma for an example of this. Again the NextJS repo provides a good example. Each endpoint reference is essentially a link that takes the developer to the API reference page.

[frederikprijck]

I added a small section for the API reference. The AuthService and AuthConfig are the main points that require elaboration on the API. The Guard and Interceptor follow Angular patterns and are not something the user interacts with.