Update readme based on 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

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

[codecov]

Codecov Report

Base: 85.71% // Head: 85.71% // No change to project coverage 👍

Coverage data is based on head (c603f1f) compared to base (b79c495).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #745   +/-   ##
=======================================
  Coverage   85.71%   85.71%           
=======================================
  Files           2        2           
  Lines           7        7           
=======================================
  Hits            6        6           
  Misses          1        1           

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[frederikprijck]

Converted back to draft as there is a typo in the banner, should be angular-jwt. The repository is named angular2-jwt, but the package is published to npm as angular-jwt in the @auth0 scope.