Add runner 2 and 3 documentations (#488)

Reviewed-on: https://gitea.com/gitea/docs/pulls/488
Reviewed-by: silverwind <[email protected]>

runner-sidebars.js

@@ -0,0 +1,45 @@
+// Sidebar of the runner documentation (develop version).
+// Released versions carry their own copy in
+// runner-docs_versioned_sidebars/version-<version>-sidebars.json.
+module.exports = {
+  runner: [
+    {
+      type: 'doc',
+      id: 'index',
+      label: 'What is the Gitea Runner?',
+    },
+    {
+      type: 'category',
+      label: 'Installation',
+      collapsed: false,
+      items: [
+        'installation/binary',
+        'installation/docker',
+        'installation/kubernetes',
+      ],
+    },
+    'registration',
+    'configuration',
+    'labels',
+    'cache',
+    'proxy',
+    {
+      type: 'category',
+      label: 'Hooks',
+      items: [
+        'hooks/job-hooks',
+        'hooks/post-task-script',
+      ],
+    },
+    'monitoring',
+    'upgrade',
+    {
+      type: 'category',
+      label: 'Reference',
+      items: [
+        'reference/cli',
+        'reference/config-example',
+      ],
+    },
+  ],
+};