docs: Add new section about Script mode, close #37

Author: peaceiris

README.md

@@ -46,6 +46,7 @@ The above example step will deploy `./public` directory to `gh-pages` branch.
   - [⭐️ Suppressing empty commits](#%EF%B8%8F-suppressing-empty-commits)
   - [⭐️ Keeping existing files](#%EF%B8%8F-keeping-existing-files)
   - [⭐️ Deploy to external repository](#%EF%B8%8F-deploy-to-external-repository)
+  - [⭐️ Script mode](#%EF%B8%8F-script-mode)
 - [Tips and FAQ](#tips-and-faq)
   - [⭐️ Use the latest and specific release](#%EF%B8%8F-use-the-latest-and-specific-release)
   - [⭐️ How to add `CNAME`](#%EF%B8%8F-how-to-add-cname)
@@ -265,6 +266,22 @@ When you use `ACTIONS_DEPLOY_KEY`, set your private key to the repository which
 
 Be careful, `GITHUB_TOKEN` has no permission to access to external repositories.
 
+### ⭐️ Script mode
+
+From `v2.5.0`, we can run this action as a shell script.
+There is no Docker build or pull step, so it will start immediately.
+
+```yaml
+- name: Deploy
+  env:
+    ACTIONS_DEPLOY_KEY: ${{ secrets.ACTIONS_DEPLOY_KEY }}
+    PUBLISH_BRANCH: gh-pages
+    PUBLISH_DIR: ./public
+  run: |
+    wget https://raw.githubusercontent.com/peaceiris/actions-gh-pages/v2.5.0/entrypoint.sh
+    bash ./entrypoint.sh
+```
+
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