docs: add github flavored markdown example to storybook

Author: ChristianMurphy

package-lock.json

@@ -49,6 +49,7 @@
     "rehype-katex": "^4.0.0",
     "rehype-raw": "^5.0.0",
     "rehype-sanitize": "^4.0.0",
+    "remark-gfm": "^1.0.0",
     "remark-math": "^4.0.0",
     "tsdx": "^0.14.0",
     "typescript": "^3.0.0"