Add annotated Dependabot configuration example

Projects repeatedly hit the same two problems when adopting Dependabot:
security updates are opened individually and ungrouped by default, so a
repository accumulates a pile of open PRs, and a freshly published
version can be pulled in before a compromised or typosquatted release
has been yanked.

Add a guideline that walks through a dependabot.yml addressing both. It
groups every ecosystem's version and security updates into a single PR
per run, and sets a 30-day cooldown that delays version updates only, so
advisory-driven security fixes still arrive immediately. Entries are
included for npm, GitHub Actions, Docker, Go modules, and cargo, along
with a note that target-branch takes no wildcards and release branches
therefore need duplicated entries.

The complete file is reproduced verbatim at the end so it can be copied
directly into .github/dependabot.yml.

Link the new page from the Security section of the project best
practices and add it to the Guidelines nav.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Ry Jones <ry@linux.com>

Author: ryjones

mkdocs.yml

@@ -135,6 +135,7 @@ nav:
   - Guidelines:
       - guidelines/index.md
       - Automated Pipelines Best Practices: guidelines/automated-pipelines-best-practices.md
+      - Dependabot Configuration Example: guidelines/dependabot-example.md
       - GitHub Contribution Guide: guidelines/github-contribution-guide.md
       - Maintainer Diversity Best Practices: guidelines/maintainer-diversity-best-practices.md
       - GitHub Organization: guidelines/github-organization.md