consider moving to x/perf/cmd/perflock

[mvdan]

The average Go developer uses the same computer to develop Go that they use to talk to other people and browse the web. So it's very normal for CPU usage to fluctuate, even when one is working.

I personally think that for this reason, perflock is as important as https://godoc.org/golang.org/x/perf/cmd/benchstat, so it should likely live in the same repository. Advantages of doing so:

• Easier to find, and more of an "official" tool
• Part of the official repos, so it's easy to contribute to (including licensing, etc)
• Improved bus factor :)

benchstat was similarly moved from https://github.com/rsc/benchstat, so I presume we could do the same here. Happy to help if any help is needed.

[mvdan]

The "easier to find" would basically mean better documentation, which is golang/go#23471.