Add note about EOL dependencies (#2890)

Inspired by the discussion here #2885, I asked some friends about it and
I want to propose this guideline: support one EOL version at a time.

MAINTAINING.md

@@ -2,26 +2,21 @@
 
 As maintainers of the gem, this is our guide. Most of the steps and guidelines in the Contributing document apply here, including how to set up your environment, write code to fit the code style, run tests, craft commits and manage branches. Beyond this, this document provides some details that would be too low-level for contributors.
 
-If you're reviewing a PR, you should ask yourself:
+If you're reviewing a PR, ask yourself:
 > * Does it work as described? A PR should have a great description.
 > * Is it understandable?
 > * Is it well implemented?
 > * Is it well tested?
 > * Is it well documented?
 > * Is it following the structure of the project?
 
+## Managing libraries dependencies EOL
+
+As a guideline for Ruby's End of Life (EOL) versions, a good heuristic (that's not too hard on maintainers) is to keep support for 1 EOL version.
+In other words, once Ruby 3.0 is EOL, drop support for 2.7.
+
 ## Security
 
 - Please review [GitHub's Good security practices for using GitHub Actions features](https://docs.github.com/en/actions/security-guides/security-hardening-for-github-actions) often.
 - Only [approve first time contributors PRs](https://github.blog/2021-04-22-github-actions-update-helping-maintainers-combat-bad-actors/) after reviewing the code carefully to prevent bad actors.
 - When merging dependabot PRs, make sure to review the changes in the PR and to check the authenticity of the bot account.
-
-### TODO
-
-- Communication
-- Workflow
-- Versioning
-- Issuing new releases
-- Updating the Changelog
-- Granting Rubygems access
-- Labeling Issues and PRs