The Rust community is large and multi-faceted. It's so large, in fact, that it can be hard to know where to go with questions or ideas. More, books at the intermediate to advanced level will often assume that readers know as much about the language community as the author does. Having been mostly on the other side of the author, reader relationship I've always found this assumption frustrating. As an author, though, I now understand the hesitancy—none of the community information will stay up to date.
Oh well. Some of this information may be out of date by the time you get to it. Reader beware.
Throughout this book, we've referred to the crates ecosystem; crates.io (https://crates.io/) is the location for Rust source projects. The docs.rs (https://docs.rs/) is a vital resource for understanding crates, and is run by the Rust team. You can also cargo docs and get a copy of your project's dependency documentation locally. I'm often without Wi-Fi, and I find this very useful.
As...