Comparative introduction to Bevy for users of other engines

Developers use other major game engines (think Unity, Unreal, Godot). Bevy should provide a smoother on-ramp for those devs that generally know what they want to do, know how to do it in X other engine, but don't know Bevy's parallel feature or approach to the same problem.

There's been no shortage of issues and discussions on the main bevy repo asking for "how to do X that I would use Y for in Unity" (i.e. bevyengine/bevy#7773). It'd definitely be useful to have a cohesive set of parallels in a well-documented place.

A landing page for each engine to help convince and convert developers to trying out Bevy is also probably a good idea, but not 100% necessary. Probably nice to have once we have a more competitive feature offering.