Improve EOL schedule for Ruby versions

[hsbt]

I'd like to improve EOL schedule each Ruby versions like:

• https://ubuntu.com/about/release-cycle
• https://devguide.python.org/versions/
• https://www.php.net/supported-versions.php
• https://github.com/nodejs/Release

We have a machine-readable data for this at https://github.com/ruby/www.ruby-lang.org/blob/master/_data/branches.yml.

[unak]

The information I think users need is:

• Clarification of Ruby's maintenance schedule principles
  • Stable version with new teeny will be released every December
  • Each teeny is scheduled to move to the security maintenance phase from April two years after the initial release of it
  • The security maintenance phase will last for 1 year, after which it will be EoL
• A cool chart showing the above for each specific version

[gotoken]

#2970 should fulfill all unak's advice. I prepared a simple benchmark. I'm not sure if the dates in _data/branches.yml for the commits are accurate, so I would appreciate it if you could check. Thanks.

[JuanitoFatas]

By the way, there is an existing service called Ruby | endoflife.date that has EOL schedule for Ruby.

[hsbt]

We can improve this at https://www.ruby-lang.org/en/downloads/branches/. I'll close this.