Update https://github.com/mozilla/pdf.js/wiki/Benchmarking-your-changes

[Snuffleupagus]

Following PRs #11807 and #11241, the "Benchmarking your changes" Wiki-page needs to be updated to account for the recent changes/simplifications; I'd suggest the following changes for the respective sections (which I've successfully used in PR #11930):

$ git checkout master
$ gulp generic
$ cd test
$ node test.js --statsFile=stats/results/baseline.json --statsDelay=5000 --manifestFile=benchmark.json

$ cd ..
$ git checkout <feature-branch>
$ gulp generic
$ cd test
$ node test.js --statsFile=stats/results/current.json --statsDelay=5000 --manifestFile=benchmark.json

Finally, it's probably a good idea to also mention the --noChrome flag on that page as well.

[timvandermeij]

Done. Thank you!