Add basic usage documentation

[realityforge]

Add usage documentation and maybe take inspiration from https://dagger.dev/users-guide.

Consider using terminology:

• Component = the values managed by the injector.
• Binding = a mechanism for creating components that can contribute to the component graph.
• Service = a java type combined with a Qualifier that describes a value that a component either consumes or publishes.
• Qualifier = an arbitrary user-supplied string that is used to distinguish between services that have the same Type but different semantics.