[README] Describe the graph viewer and its usage - #162

Rule: merge [bot] PRs when CI pass (merge)

• -closed [📌 merge requirement]
• any of:
  • author = dependabot[bot]
  • author = gepetto-flake-updater[bot]
  • author = github-actions[bot]
  • author = hrp2-14
  • author = pre-commit-ci[bot]
• -conflict [📌 merge requirement]
• -draft [📌 merge requirement]
• check-success = "check-macos-linux-nix"
• check-success = "check-ros-ci"
• check-success = "pre-commit.ci - pr"
• any of: [📌 merge -> configuration change requirements]
  • -mergify-configuration-changed
  • check-success = @mergify/Configuration changed
  • check-success = @mergify/Configuration has been deleted

More conditions and actions can be found in the documentation.

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• @Mergifyio refresh will re-evaluate the rules
• @Mergifyio rebase will rebase this PR on its base branch
• @Mergifyio update will merge the base branch into this PR
• @Mergifyio backport <destination> will backport this PR on <destination> branch

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• look at your merge queues
• generate the Mergify configuration with the config editor.

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