document running a mix alpha/beta/stable in your environment

[philips]

A common question we get asked is what version of CoreOS Linux should we run in prod. The tl;dr is:

"Stable, but please mix in a few beta (and alpha) nodes so you know what is coming down the pipeline that might break your stable environment."

We should document this somewhere though. cc @crawford

[robszumski]

Not that this is enough, but on https://coreos.com/releases the Beta channel description is:

The Beta channel consists of promoted Alpha releases. Mix a few beta machines into your production clusters to catch any bugs specific to your hardware or configuration.

[bgilbert]

We should make a point of emphasizing this in the Container Linux quickstart docs. Regressions that affect particular environments are often reported only after they reach stable, which implies that the affected users are not following the advice above. Right now we're only giving that advice on the releases page, and even there we don't say it very loudly.