message: docs: update relative perf test readme
diff: ### Benchmark instructions.
  -1. `npm run quick-build` in packages/chevrotain
  +1. `yarn run quick-build` in packages/chevrotain
  - This will generate chevrotain.js artifact in the lib directory.
  -2. open both index_dev.html and index_latest.html
  +2. open both index_dev.html and index_latest.html in your prefered browser.
  3. Select the running mode (lex/parse or both) by clicking the relevant button.
  - You should run both scenarios (Dev/Latest) in the same mode
  - You should run the `Latest` mode first as the Dev results are compared against it (via localStorage).
  + - It is recommended to run each scenario a **few times** to let the browser JS fully optimize both scenarios.
  