[DOC] Use npm start, not yarn start to start

[eguiraud]

yarn start --production ignores the --production flag,
npm start --production does not.

[eguiraud]

Resolved conflicts, ready to merge

[ccoenen]

I know this was already merged, but shouldn't we also update

https://github.com/codimd/server/blob/313eb74ed697c5260df9293b1aefe3695cf65a5a/bin/setup

at the same time? If we stop using yarn (which I'm perfectly fine with!) we should also remove it from the setup script.

[eguiraud]

I can't comment on dropping yarn altogether. There are still calls to yarn in the manual setup instructions. The PR only changed yarn start to npm start because otherwise the --production flag is ignored.

This might very well be a bug in yarn that they will fix in a next release, I don't know.

[SISheogorath]

I don't think we want to remove yarn, but just use npm for for the production start (since in yarn it simply doesn't work as with npm). When recently someone went through all files and replaced npm with yarn, it was unnoticed that npm start --production is fundamentally different from yarn start --production.

[ccoenen]

ok, got it :-)