Document Required: RwLock in this crate compared to the RwLock in parking_lot/std

[YjyJeff]

Hi, I am curious about why the dashmap is so fast, therefore, I am reading the source code and docs to figure it out.

I find that sharding is a common technique used to implement the concurrent hashmap. From the implementation view, RwLock implemented in this crate is the main technique to make it unique, compared to other concurrent hashmaps. However, the RwLock does not have docs to describe the difference between it and RwLock in parking_lot/std. Could you add the docs to describe the benefits of this RwLock compared to parking_lot/std and why it is implemented in this way? It is really helpful for me

Thanks in advance