add docs-centralizer CI job

.drone.yml

@@ -1,4 +1,29 @@
 ---
+# SPDX-FileCopyrightText: 2022 Free Software Foundation Europe <https://fsfe.org>
+#
+# SPDX-License-Identifier: CC0-1.0
+
+# sync the documentation with docs.fsfe.org
+kind: pipeline
+name: syncdocs
+
+steps:
+  - name: push-to-docs
+    image: git.fsfe.org/fsfe-system-hackers/docs-centralizer:latest
+    environment:
+      REPO_NAME: innernet-playbook
+      SSH_PRIVATE_KEY:
+        from_secret: docs_bot_private_key
+    when:
+      branch:
+        - master
+      event:
+        - push
+
+# Define the docker host ("drone runner node") on which this will be executed
+node:
+  cont: test
+---
 kind: pipeline
 type: docker
 name: test LDAP connection

README.md

@@ -1,3 +1,5 @@
+[![in docs.fsfe.org](https://img.shields.io/badge/in%20docs.fsfe.org-OK-green)](https://docs.fsfe.org/repodocs/innernet-playbook/00_README)
+
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 **Table of Contents**