Stokes Drift Docs/Physics page does not include 3D Stokes implementation

[navidcy]

At the moment the docs only mention the uniform unidirectional Stokes drift implementation

https://clima.github.io/OceananigansDocumentation/stable/physics/surface_gravity_waves/

We need to update the docs to take into account the 3D Stokes implementation that was introduced with #3384.

cc @BrodiePearson @glwagner @LeeAra0