Add the Discourse meaning of beta to the install doc

If you grew up in a Microsoft environment, the word beta sounds like :scream::spider::cloud_with_lightning::ambulance:

With the excellent 30 minute install document I got it working without a glitch and it has been running fine for a week now. But my hart missed a few beats when I just saw that I got v2.0.0.beta3…

Maybe a few words should be added to the document explaining what has been replied in these older topics:


This has been discussed in other topics that already exist.