Document `Container.Decorator`

[squirly]

Simple example:

export const bindDependencies = Container.Decorator<
  // the dependencies made available ("exported")
  ExportedDependency,
  // The dependencies required for the dependencies being added
  RequiredDependency1 | RequiredDependency2,
> = container => container
    // dependencies added here do not have to be "exported"
    .bindService(PrivateDependency, PrivateDependency)
    .bindService(ExportedDependency, ExportedDependency);