Provide basic usage examples in the documentation

[garma83]

As in title. I have the feeling you guys might be seriously underestimating the importance of this.

Examples required:

• how to get the distance between points, or a point and a segment
• how to do intersections between segments
• how to do ray casting, and get the intersecting point
• how to use the polygon shape (figuring out whether it is closed loop, doing intersections etc)

Even if you just 'dump' say 10 code examples in the index of the documentation, that would already go a long way.

[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)