Add a section in the README that explains how to add new features to the new design.

[tvpeter]

Describe the enhancement

To enable new contributors easily understand and add new features to the redesigned architecture, add a section in the documentation that shows how a new command can be added and it should contain code snippets.

Use case

• Help new contributors understand components of the project
• Help them be able to add new features

Additional context

See #278