Add API json documentation on root

web/pages/api/index.js

+export default function handler(req, res) {
+  res.status(200).json(
+    { 
+      name: 'Nansen API',
+      services: [
+        {
+          name: 'Collection',
+          url: '/api/collection',
+          description: 'Top level Nansen IIIF collection manifest'
+        },
+        {
+          name: 'Collection ID',
+          url: '/api/collection/[id]',
+          description: 'Get IIIF collection manifest for a Group owning objects used in the exhibition.',
+          example: '/api/collection/782c5364-7324-4f16-b5af-2c60b73fc707'
+        },
+        {
+          name: 'Manifest ID',
+          url: '/api/manifest/[id]',
+          description: 'Get IIIF manifest for HumanMadeObject stored in the exhibition database, e.g. not imported from external source.',
+          example: '/api/manifest/4eb0facf-8d5a-44cc-94ea-71ffe70fcc46'
+        }
+      ]
+    }
+  )
+}
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