Rename FB Internal to Under the Hood

Summary:
I think there's a need for an "implementation details" section of the site. Especially as we're moving the rest of our wiki content there.

I see it as a good thing, because now we have a place for implementation details relevant to OSS contributors too, it's not all fb-specific.

Reviewed By: nikoant

Differential Revision: D25614909

fbshipit-source-id: 5ec081e6450a9ad1c30785ae4cca74b6fa0d2630

website/sidebars.js

@@ -115,27 +115,29 @@ module.exports = {
       'extending/layout-inspector',
     ],   
   },
-  'fb-internal': {
-    'FB Internal': fbInternalOnly([
-      'fb/index',
+  internals: {
+    Internals: [
+      'internals/index',
       'extending/public-releases',
-      'fb/release-infra',
-      'fb/LauncherConfig',
-      'fb/hacking-on-launcher',
-      'fb/Flipper-fbsource-Pinning',
-      'fb/Flipper-Release-Cycle',
-      'fb/Add-Support-Group-to-Flipper-Support-Form',
-      'fb/Help-Updating-Flipper',
       'extending/testing-rn',
-      'fb/Alerts',
-      'fb/bundling',
-      'fb/Certificate-Exchange-Diagram',
-      'fb/Electron-Upgrade',
-      'fb/flipper-analytics',
-      'fb/Navigation-Plugin-Development-Guide',
-      'fb/Oncall-Runbook',
-      'fb/sandcastle',
-      'fb/Star-Ratings',
-    ]),
+      ...fbInternalOnly([
+        'fb/release-infra',
+        'fb/LauncherConfig',
+        'fb/hacking-on-launcher',
+        'fb/Flipper-fbsource-Pinning',
+        'fb/Flipper-Release-Cycle',
+        'fb/Add-Support-Group-to-Flipper-Support-Form',
+        'fb/Help-Updating-Flipper',
+        'fb/Alerts',
+        'fb/bundling',
+        'fb/Certificate-Exchange-Diagram',
+        'fb/Electron-Upgrade',
+        'fb/flipper-analytics',
+        'fb/Navigation-Plugin-Development-Guide',
+        'fb/Oncall-Runbook',
+        'fb/sandcastle',
+        'fb/Star-Ratings',
+      ]),
+    ],
   },
 };