Create horizon-worlds.md

[TylerMWise]

Changes

I have added info for Meta Horizon Worlds developers, showing what Roblox has compared to that

Having used it, and reading this (https://developers.meta.com/horizon-worlds/learn/documentation/get-started/meta-horizon-worlds-for-roblox-creators) I believe it has most of the needed info. It does need pictures tho

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[TylerMWise]

Updated v2

[aetter]

Hey @TylerMWise, thanks a bunch for the PR -- really appreciate all the work here. That said, I don't think it's a good fit for the docs. The existing Unity and Unreal pages were in response to a sizable number of requests from developers; we're looking to meet our audience where they are rather than add comparisons to every other engine out there. Thanks again!