Update index.mdx

[warnessa]

Add new file type support

Summary

added new download/upload file type support. Under exectuables .pkg, msix, and appx have been added. Also created a new section titled "system". under there we now have dmg

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) — how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The documentation style guide has been adhered to.

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