Some demo example links only function when developing x-element

[klebba]

A dead simple starting point for custom elements.

Examples

- [chess piece](http://localhost:8080/@netflix/x-element/demo/chess)
- [integrating with lit-html](http://localhost:8080/@netflix/x-element/demo/lit-html)
- [integrating with µhtml](http://localhost:8080/@netflix/x-element/demo/uhtml)
- [wrapping in react](http://localhost:8080/@netflix/x-element/demo/react)
- [run tests](http://localhost:8080/@netflix/x-element/test)
- [performance](http://localhost:8080/@netflix/x-element/demo/performance)

The run tests and performance links will not function post-installation — we should consider moving these off to /dev or some other subfolder to avoid confusion/frustration

GET http://localhost:8080/@netflix/x-element/node_modules/@netflix/x-test/x-test.js net::ERR_ABORTED 404 (Not Found)

GET http://localhost:8080/@netflix/x-element/demo/performance/default.html?test=inject 500 (Internal Server Error)

Error 500: Unknown MIME type for file extension: .html?test=inject