Readme.md references `File.lock`, which doesn't seem to be a thing

[maxjacobson]

First of all, thanks for this very useful gem!

Regarding this from the Readme.md:

Running setup or teardown once

require "parallel_tests"

# preparation:
# affected by race-condition: first process may boot slower than the second
# either sleep a bit or use a lock for example File.lock
ParallelTests.first_process? ? do_something : sleep(1)

AFAICT, File.lock is not part of the Ruby standard library. Is it perhaps from a gem? I do see File#flock, but I'm not too familiar with it. Maybe that's what this was referring to?

It would be helpful to have a working example with a lock if possible.

[grosser]

👁 #1013

... I did not come up with a good flock example, so just using File.write/read