Documented so far undocumented top level APIs

Summary: Per title

Reviewed By: passy

Differential Revision: D24992066

fbshipit-source-id: a9aa351600d46a67b605e8555efb30d42ffc2d9b

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -22,6 +22,8 @@ test('Correct top level API exposed', () => {
       exposedAPIs.push(key);
     }
   });
+
+  // Note, all `exposedAPIs` should be documented in `flipper-plugin.mdx`
   expect(exposedAPIs.sort()).toMatchInlineSnapshot(`
     Array [
       "Layout",
@@ -34,6 +36,7 @@ test('Correct top level API exposed', () => {
       "useValue",
     ]
   `);
+
   expect(exposedTypes.sort()).toMatchInlineSnapshot(`
     Array [
       "Atom",