src/pages/index.astro should check user's locale when redirecting instead of assuming en-US

https://github.com/AscensionGameDev/Intersect-Documentation/blob/main/src/pages/index.astro#L18

The following might be usable to grab the user's preferred languages, and we can cross-reference that against our enabled language codes to redirect them properly:
https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/i18n/getAcceptLanguages