Docusarus: Init Project (#1312)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1312

This starts us transitioning the Yoga website off of an ancient version of Gatsby by initializing a new Docusaurus project. This commit adds a new stock project, to be filled in later, then fixes license lint errors.

Note that this seems to have init'd using npm, but in the next diff I convert this to yarn workspaces anyway.

Reviewed By: yungsters

Differential Revision: D46884434

fbshipit-source-id: 7a0a4dddc144ad2d22cd18a02e8dcb9ff2184489

website-next/docs/tutorial-basics/create-a-page.md

@@ -0,0 +1,43 @@
+---
+sidebar_position: 1
+---
+
+# Create a Page
+
+Add **Markdown or React** files to `src/pages` to create a **standalone page**:
+
+- `src/pages/index.js` → `localhost:3000/`
+- `src/pages/foo.md` → `localhost:3000/foo`
+- `src/pages/foo/bar.js` → `localhost:3000/foo/bar`
+
+## Create your first React Page
+
+Create a file at `src/pages/my-react-page.js`:
+
+```jsx title="src/pages/my-react-page.js"
+import React from 'react';
+import Layout from '@theme/Layout';
+
+export default function MyReactPage() {
+  return (
+    <Layout>
+      <h1>My React page</h1>
+      <p>This is a React page</p>
+    </Layout>
+  );
+}
+```
+
+A new page is now available at [http://localhost:3000/my-react-page](http://localhost:3000/my-react-page).
+
+## Create your first Markdown Page
+
+Create a file at `src/pages/my-markdown-page.md`:
+
+```mdx title="src/pages/my-markdown-page.md"
+# My Markdown page
+
+This is a Markdown page
+```
+
+A new page is now available at [http://localhost:3000/my-markdown-page](http://localhost:3000/my-markdown-page).