[Blocking] README layout: add Quickstart and move reference docs to docs/ #69

Blocking (doc-reviewer): The root README has no ## Quickstart, holds the inputs reference and testing notes inline, and docs/ does not exist.

• README.md:10: rename ## Usage to ## Quickstart with numbered steps: (1) create the SETTINGS_GUARD token with read and admin permissions, (2) add .github/workflows/settings-guard.yml with the example.
• README.md:52: move the inputs table (lines 52-76) to docs/configuration.md.
• README.md:81: move the Testing section to docs/development.md (or docs/testing.md).
• Add a ## Documentation section linking every docs/*.md page.

Location:

• settings-action/README.md

  Line 10 in a276963

  ## Usage

• settings-action/README.md

  Lines 52 to 76 in a276963

  	use the following variables:
  	| Option | Description |
  	| ------------------------------------------------------------ | -------------------------------------------------------------------------------------------------------------------------------------- |
  	| debug | Enable debug logging |
  	| description | Change the description of a GitHub repository |
  	| project | The owner/repo |
  	| settings_actions_allowed_actions | Actions permissions: `all`, `local_only`, or `selected`. Use `selected` to allow OWNER + specific non-OWNER actions/reusable workflows |
  	| settings_actions_github_owned_allowed | When `settings_actions_allowed_actions` is `selected`, whether GitHub-owned actions (e.g. `actions/checkout`) are allowed |
  	| settings_actions_verified_allowed | When `settings_actions_allowed_actions` is `selected`, whether actions from verified creators are allowed |
  	| settings_actions_patterns_allowed | When `settings_actions_allowed_actions` is `selected`, comma-separated list of allowed actions/reusable workflows (e.g. `030/*`) |
  	| settings_actions_require_sha_pinning | Require actions to be pinned to a full-length commit SHA |
  	| settings_default_workflow_permissions | Set the default workflow permissions to read or write |
  	| settings_delete_branch_on_merge | Delete a branch on merge or not |
  	| settings_discussions | Enable the discussions tab or not |
  	| settings_github_workflows_can_approve_pull_request_reviews | Whether workflows can approve pull requests |
  	| settings_merge_commit | Enable merge commit |
  	| settings_merge_rebase | Enable merge request rebase |
  	| settings_merge_squash | Enable merge request squash |
  	| settings_protect_main_branch | Protect the main branch or not |
  	| settings_protect_main_branch_enforce_admins | Enforce branch protection for admins |
  	| settings_protect_main_branch_required_approving_review_count | The number of approvals that is required before a PR can be merged |
  	| settings_projects | Whether the project tab should be enabled |
  	| settings_wiki | Wiki enabled or not |
  	| topics | The topic(s) that will appear in the about menu of a project |

• settings-action/README.md

  Line 81 in a276963

  ## Testing

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