Doc: update release documentation with the latest

[TrueBrain]

Motivation / Problem

During 14.0 release cycle I noticed that the release documentation was slightly out of date.

Description

Fix a few mentions:

• Website workflow has changed; no need to tag anymore.
• Preview of website post can be seen via a link on the PR page itself (no need to go to Checks)
• Updated the amount of socials we use

Further more, I noticed that it wasn't really spelled out how to do Steam / GOG. So I spend a few words on that. Ofc people can still ask me to do so. But having it documented means someone else might also ;)

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker