docs(readme): link maintenance runbook docs in Documentation table

[ulises-jeremias]

Context

cpa-templates/docs/ includes maintenance runbooks (MAINTENANCE_*.md) that are not linked from the README Documentation table. Contributors miss them.

Steps

1. List markdown files under docs/.
2. Add rows to the README Documentation table for each maintenance doc that is missing.
3. Write a one-sentence summary per doc (mirror the existing table tone).

Acceptance criteria

• Links for MAINTENANCE_RUNBOOK.md, MAINTENANCE_TEMPLATES.md, MAINTENANCE_CI.md, MAINTENANCE_DEPENDENCIES.md, MAINTENANCE_SECURITY.md, MAINTENANCE_RELEASE.md (add any other missing docs you find)
• Each row has an accurate one-line blurb
• Links resolve on main

Files

• README.md
• docs/MAINTENANCE_*.md (reference)

How to verify

Click each new link from the rendered README.