add ReactComponentContent demo

docs/src/demos/Guide/NodeViews/ReactComponentContent/index.jsx

@@ -0,0 +1,29 @@
+import React from 'react'
+import { useEditor, EditorContent } from '@tiptap/react'
+import { defaultExtensions } from '@tiptap/starter-kit'
+import ReactComponent from './Extension.js'
+import './styles.scss'
+
+export default () => {
+  const editor = useEditor({
+    extensions: [
+      ...defaultExtensions(),
+      ReactComponent,
+    ],
+    content: `
+    <p>
+      This is still the text editor you’re used to, but enriched with node views.
+    </p>
+    <react-component>
+      <p>This is editable.</p>
+    </react-component>
+    <p>
+      Did you see that? That’s a React component. We are really living in the future.
+    </p>
+    `,
+  })
+
+  return (
+    <EditorContent editor={editor} />
+  )
+}