Mention hyperbolized Serre-Green-Naghdi equations

[JoshuaLampert]

I just noticed that we don't mention the hyperbolized form of the Serre-Green-Naghdi equations in the README and the docs.

[github-actions]

Benchmark Results

	main	5dea2e8...	main/5dea2e8d115d1b...
bbm_1d/bbm_1d_basic.jl	13.9 ± 0.36 μs	13.8 ± 0.3 μs	1.01
bbm_1d/bbm_1d_fourier.jl	0.215 ± 0.011 ms	0.268 ± 0.051 ms	0.803
bbm_bbm_1d/bbm_bbm_1d_basic_reflecting.jl	0.117 ± 0.0017 ms	0.122 ± 0.0027 ms	0.963
bbm_bbm_1d/bbm_bbm_1d_dg.jl	0.0342 ± 0.00051 ms	0.0346 ± 0.00048 ms	0.99
bbm_bbm_1d/bbm_bbm_1d_relaxation.jl	27.8 ± 0.44 μs	27.2 ± 0.37 μs	1.02
bbm_bbm_1d/bbm_bbm_1d_upwind_relaxation.jl	0.0485 ± 0.00045 ms	0.0491 ± 0.00068 ms	0.989
hyperbolic_serre_green_naghdi_1d/hyperbolic_serre_green_naghdi_dingemans.jl	4.13 ± 0.013 μs	4.23 ± 0.014 μs	0.976
serre_green_naghdi_1d/serre_green_naghdi_well_balanced.jl	0.199 ± 0.0044 ms	0.197 ± 0.0053 ms	1.01
svaerd_kalisch_1d/svaerd_kalisch_1d_dingemans_relaxation.jl	0.146 ± 0.0035 ms	0.143 ± 0.0025 ms	1.02
time_to_load	1.99 ± 0.0088 s	2 ± 0.011 s	0.997

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.