Improve release verification instructions

[andygrove]

Is your feature request related to a problem or challenge?

The release verification instructions do not specify that we need to increase the Rust stack size. For example, I had to set RUST_MIN_STACK=3000000 for the tests to pass with 37.0.0-rc1.

We also need to set ulimit -n to make sure enough file handles are available.

It may also be useful to be able to control the number of threads used in cargo test when running the verification script.

Describe the solution you'd like

Improve the documentation

Describe alternatives you've considered

No response

Additional context

No response

[alamb]

I also hope that work related to #9637 will improve this symptom / reduce the need for the large stacks in debug builds

[waynexia]

I observed the peak memory usage increases with RUST_MIN_STACK=3000000. It looks more expensive than 3MB...