Reorganise extend sidebar

Summary:
- Layout was in an odd spot. "Other platforms" is still weird, but it's at least next to the JS part now.
- Tutorial is the first thing after the intro.

Reviewed By: danielbuechele

Differential Revision: D15198470

fbshipit-source-id: 263582ee51f228a295be5952f5dc219e53c5e3e6

website/i18n/en.json

@@ -148,8 +148,8 @@
       "Plugin Setup": "Plugin Setup",
       "Advanced Usage": "Advanced Usage",
       "Extending Flipper": "Extending Flipper",
-      "Plugin Development": "Plugin Development",
       "Tutorial": "Tutorial",
+      "Plugin Development": "Plugin Development",
       "Other Platforms": "Other Platforms",
       "Internals": "Internals"
     }

website/sidebars.json

@@ -29,7 +29,13 @@
     "Advanced Usage": ["custom-ports", "stetho"]
   },
   "extending": {
-    "Extending Flipper": ["extending/index", "extending/layout-inspector"],
+    "Extending Flipper": ["extending/index"],
+    "Tutorial": [
+      "tutorial/intro",
+      "tutorial/android",
+      "tutorial/js-table",
+      "tutorial/js-custom"
+    ],
     "Plugin Development": [
       "extending/js-setup",
       "extending/js-plugin-api",
@@ -43,17 +49,14 @@
       "extending/testing",
       "extending/debugging"
     ],
-    "Tutorial": [
-      "tutorial/intro",
-      "tutorial/android",
-      "tutorial/js-table",
-      "tutorial/js-custom"
-    ],
     "Other Platforms": [
       "extending/new-clients",
       "extending/establishing-a-connection",
       "extending/supporting-layout"
     ],
-    "Internals": ["extending/arch"]
+    "Internals": [
+      "extending/arch",
+      "extending/layout-inspector"
+    ]
   }
 }