Update docs with Trixi examples

After the PRs in [Trixi.jl ](https://github.com/trixi-framework/Trixi.jl/pull/2379)and [TrixiShallowWater.jl](https://github.com/trixi-framework/TrixiShallowWater.jl/pull/96) are merged that migrate all the shallow water functionality into the TrixiShallowWater.jl package, the documentation and example elixirs herein need adjusted.