Provide basic usage examples in the documentation about parry

[EriKWDev]

I agree the documentation is very bare bones, but shout-out to the examples directory https://github.com/dimforge/parry/tree/master/crates/parry2d/examples as well as the tests at https://github.com/dimforge/parry/tree/master/crates/parry2d/tests

More complete examples would be nice. Perhaps more of a complete demo like a platformer using some rendering library like macroquad together with physics from parry would go much further in terms of how to actually use the library, not just demonstrating that it works in very limited examples.

Also, having the "gatting started" guide tell us nothing more than how to add the dependency to Cargo.toml would be appreciated xP (https://parry.rs/docs/user_guide/getting_started)