Create forge cast commands to interact with the waterfalls

[OisinKyne]

Problem to be solved

When we deploy the factory, we want to make it easy for people to use it

Proposed solution

Deploy the factory.

Document the forge/foundry/cast command needed to call the createWaterfall type functions.

Outline how to create different waterfalls with different SplitWallets underneath.

[boulder225]

Please add your planning poker estimate with Zenhub @samparsky

[samparsky]

@OisinKyne This should be replaced by interacting with the factory via Etherscan as using cast would require encoding args and it becomes complex really fast