Improve reference overview diagrams

[andreivladbrg]

I've been reviewing the diagrams and I think they are a little bit misleading.

For example, the create a stream diagram is making me believe that:

1. The Proxy has a create function
2. The Proxy Target directly calls the core contract
3. ERC-20 assets will be held in Permit2 contract

All three points from above are incorrect.

The first two points can be also applied to sender-withdraws diagram:

As well, I would say that changing the final node for recipient would be more appropriate, with the connecting line indicating something like ERC20-transfer.

[PaulRBerg]

Agree with your suggestion!