doc: add tokio-console page in book dev section (#4641)

* doc: add tokio-console page in dev section

* Add screenshot

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

book/src/dev/tokio-console.md

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+# `tokio-console` support
+
+`tokio-console` is a diagnostics and debugging tool for asynchronous Rust programs. This tool can be
+useful to lint runtime behavior, collect diagnostic data from processes, and debugging performance
+issues. ["it's like top(1) for tasks!"][top]
+
+### Setup
+
+Support for `tokio-console` is not enabled by default for zebrad. To activate this feature, run:
+ ```sh
+ $ RUSTFLAGS="--cfg tokio_unstable" cargo build --no-default-features --features="tokio-console" --bin zebrad
+ ```
+
+Install [`tokio-console`][install].
+
+Then start `zebrad` however you wish.
+
+When `zebrad` is running, run:
+```
+$ tokio-console
+```
+
+The default options are used, so `tokio-console` should connect to the running `zebrad` without other configuration.
+
+### Example
+
+<img width="788" alt="image" src="https://user-images.githubusercontent.com/552961/174457604-53c6ffc6-64f6-4952-94c6-ac7eb37c3871.png">
+
+
+### More
+
+For more details, see the [`tokio` docs][enabling_tokio_instrumentation].
+
+
+[top]: https://github.com/tokio-rs/console#extremely-cool-and-amazing-screenshots
+[install]: https://github.com/tokio-rs/console#running-the-console]
+[enabling_tokio_instrumentation]: https://github.com/tokio-rs/console/blob/main/console-subscriber/README.md#enabling-tokio-instrumentation
+