Rework the "Stay tuned" section of the "Download" page

Originally created by @sajolida on #7163 (Redmine)

Lately, I’ve try to simplify “Download” page to make it more efficient.

I’ve already moved the installing instructions to the “First steps”
section of the documentation. Now I’m questioning the point of the “Stay
tuned” section as:

1. Automatic upgrades are enabled by default. And that seems to really
work because I’ve seen way less outdated version in WhisperBack bug reports.

2. Our “News” page is displayed by default when opening the browser and
its header duplicate some of that information. Still, this fact has been
questioned in ticket #7023.

So, shall we strip down this section? remove it all the way?

Feature Branch: doc/stay-tuned