Guide for using RR with CPython

rr is a record & replay debugging tool. I've found it particularly helpful for debugging multiprocessing issues, free-threading bugs, and non-deterministic crashes.

@ericsnowcurrently suggested adding a devguide entry for how to use rr specifically for CPython development. That seems like a good idea to me.

Here are some topics I think are worth covering:

• How to install rr? The OS provided packages (e.g., Ubuntu) are often out-of-date and may not work well with some CPython test suites or new CPUs. The latest release on GitHub is much better: https://github.com/rr-debugger/rr/releases/
• How to use rr for multiprocessing? (rr replay -p pid or rr replay -f pid)
• How to use rr for multi-threading issues?
• How to use rr to track down intermittent crashes? (Roughly, record lots of traces until you find a crasher).