docs(createMachine): Add `section`, fix case in `permalink`

Looks like your build _really_ likes lowercase URLs, so that’s why I changed `permalink`. The other API pages all seem to have the `section` entry in their frontmatter too, so I added it. **Note:** I looked into this because I noticed that the “breadcrumbs” for the `createMachine` page still shows it as if it it’s part of “Core Concepts”. I don’t know Astro, so I don’t know if this will fix it. Here’s hopin’! (P.S.: Thanks for fixing the deployed site! Yay! 👍)