docs-bug(Github README): Update "What we're working on" section

[anisabboud]

Documentation Feedback

The project README "What we're working on now (Q4 2021)" section hasn't been updated in the past year.

I think it's important to keep the main README up-to-date, to avoid misleading new developers who might think the project isn't updated even though it's very active with major recent changes.

Maybe add links to recent posts/videos:

• https://material.angular.io/guide/mdc-migration Migrating to MDC-based Angular Material Components
• https://youtu.be/XlPtyPb3Hmw What's new in Angular Material and the CDK in Angular v15
• https://youtu.be/d6FJg2MW-lI Building accessible Angular apps

Affected documentation page

https://github.com/angular/components