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/blog/2021-08-01-mdx-blog-post.mdx

@@ -0,0 +1,20 @@
+---
+slug: mdx-blog-post
+title: MDX Blog Post
+authors: [slorber]
+tags: [docusaurus]
+---
+
+Blog posts support [Docusaurus Markdown features](https://docusaurus.io/docs/markdown-features), such as [MDX](https://mdxjs.com/).
+
+:::tip
+
+Use the power of React to create interactive blog posts.
+
+```js
+<button onClick={() => alert('button clicked!')}>Click me!</button>
+```
+
+<button onClick={() => alert('button clicked!')}>Click me!</button>
+
+:::