ルート配下に admin　ファイルを作成しその中に index.htmlとconfig.ymlを作成するだけでインストールすることができる。

index.html

<!doctype html>
<html>
<head>
    <meta charset="utf-8"/>
    <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
    <title>Content Manager</title>
    <style type="text/css">
        .SplitPane.css-gwx01d-StyledSplitPane-dropMain-card-splitPane.e1pxf6c40.vertical  {
            display: flex;
            flex-direction: column !important;
            overflow: auto !important;
        }
        .Pane.vertical.Pane1{
            width: 100% !important;
        }
    </style>
</head>
<body>
<!-- Include the script that builds the page and powers Netlify CMS -->
<script src="https://unpkg.com/netlify-cms@^2.0.0/dist/netlify-cms.js"></script>
<script src="https://identity.netlify.com/v1/netlify-identity-widget.js"></script>
<script>
    if (window.netlifyIdentity) {
        window.netlifyIdentity.on("init", user => {
            if (!user) {
                window.netlifyIdentity.on("login", () => {
                    document.location.href = "/admin/";
                });
            }
        });
    }
</script>
</body>
</html>

config.yml

backend:
  name: git-gateway
  repo: [git-repo]   #githubのリポジトリ
  branch: [ブランチ]  # Branch to update (optional; defaults to master)

publish_mode: editorial_workflow

media_folder: "static/images/uploads" #アップロードされたファイルを保存するフォルダパス
public_folder: "/images/uploads" #アップロードされたファイルがアクセスされるフォルダパス
collections:
  - name: "post"
    label: "Post"
    folder: "content/post"
    create: true
    slug: "{{slug}}"
    fields: # 管理画面に追加したいフォームを追加していく
      - {label: "Title", name: "title", widget: "string"}
      - {label: "Description", name: "description", widget: "text", required: false}
      - {label: "Featured Image", name: "featuredImage", widget: "image", required: false}
      - {label: "Featured Image Description", name: "featuredImageDescription", widget: "text", required: false}
      - {label: "Publish Date", name: "date", widget: "datetime"}
      - {label: "Category", name: "categories", widget: "text", required: false}
      - {label: "Tag", name: "tag", widget: "text", required: false}
      - {label: "Body", name: "body", widget: "markdown"}