Document first time setup

bbrala → credited jjchinquist → .

bbrala → credited mupsi → .

bbrala → credited nicoloye → .

So after mostly others working on this in the contrib room. The conclusion is that inital installation docs with using the existing database are a bad idea. Doing a site install with the existing config flag saves us loads of time.

So im updateing the docs.

adding jjchinquist, nicoloye, mupsi to credits, since they had the most pain today because of this.

Updated docs the the latest conclusion of the day. <3

I'm taking a look at this today, trying to set it up locally, so once I finish I'll share my feedback :)

Can someone explain to me how to run this gitlab job? I was looking at this with @vrancje and we couldn't see it right away. This should also be documented