fixed incorrect comments

[mixed]

When I build fail, I saw below message. I think that below comment is wrong.

yarn install; yarn build;

[patrickhulce]

ah, the commands to run depend on which directory you're in @mixed :)
It's true the more common case will likely be running into this issue when developing lighthouse core rather than just chrome-launcher. We could also alias 'install-launcher' and 'build-launcher' in the launcher repo to run the regular commands, haha. thoughts @samccone?

[mixed]

Thanks @patrickhulce

I got it. :) I ran into the root folder and met the message. If I ran it in the chrome-launcher folder, it would not have been a problem. If so, I hope that it will be modified as well.

[paulirish]

this lgtm
it's in line with our similar check over here: https://github.com/GoogleChrome/lighthouse/blob/master/lighthouse-cli/compiled-check.js