Doc Improvements

[jayanderson]

Answering these questions will probably just need doc improvements rather than other fixes, but I'm not sure so here goes:

• Using cargo profiler callgrindwhich executable is run?
• How does this work with cargo bench? Can I run cargo profiler --bench callgrind (or something like that) to get profile stats for the different benchmarks? For now I've been creating a main.rs building that (with debug symbols) and then using cargo profiler callgrind -n 20 --bin ./target/release/executable_name. I swap out the contents of main with my benchmarks to get results. This seems suboptimal. I'm probably missing something.
• It's probably worth calling out specifically that -n <count> limits the shown instructions. That wasn't immediately clear.

Thanks.

[MagaTailor]

The profiled binary comes from the build command.

Normally, rust benchmarks are separate binaries running with or without the --bench flag. This means, at least for now, you can profile benchmarks using the --bin flag (optionally with command line arguments via --)