Would love to see the supervisor and registry in the user guide.

[f8122dac91]

Hello!

We love actix actor framework and we've been using it in our production development for an year now. We've been using the registry functionality in our code, and mostly been reading the API documentation and the code to figure out how to use the features, but it would be really nice if these features were explained by the developers in the user guide.

[SeedyROM]

^ 100% agreed! 👍

Also if this isn't something that you think will be written into the book, could you provide some good examples at the very least?