Don't mention npm command for installation

[SyntaxColoring]

The v4.3.1 release notes say:

Also note that the npm package manager is no longer officially supported by The Lounge and we now only support using yarn.

I take this to mean that we should always install with yarn global add, and never with npm install --global. That would mean that this mention of npm install --global on the "Install and upgrade" page is obsolete. So, remove it.

I'm unfamiliar with Javascript package management, so forgive me if I've missed the point!

[SyntaxColoring]

There's another mention right below:

Note that installing from npm or yarn does not daemonize nor autostart The Lounge.

Not sure if it's better to leave that one in or take it out.

[brunnre8]

7e936c2

[brunnre8]

Thank you