add favicon

[ranocha]

I created an ico file from the logo added in #239 using GIMP.

[github-actions]

Benchmark Results (Julia v1.10)

Time benchmarks

	main	10e8528...	main / 10e8528...
bbm_1d/bbm_1d_basic.jl - rhs!:	13.8 ± 0.33 μs	14 ± 0.38 μs	0.983 ± 0.036
bbm_1d/bbm_1d_fourier.jl - rhs!:	0.528 ± 0.19 ms	0.215 ± 0.0089 ms	2.46 ± 0.9
bbm_bbm_1d/bbm_bbm_1d_basic_reflecting.jl - rhs!:	0.0807 ± 0.00026 ms	0.0804 ± 0.00041 ms	1 ± 0.0061
bbm_bbm_1d/bbm_bbm_1d_dg.jl - rhs!:	0.034 ± 0.00046 ms	0.0345 ± 0.00051 ms	0.986 ± 0.02
bbm_bbm_1d/bbm_bbm_1d_relaxation.jl - rhs!:	27.3 ± 0.49 μs	28.4 ± 0.72 μs	0.961 ± 0.03
bbm_bbm_1d/bbm_bbm_1d_upwind_relaxation.jl - rhs!:	0.0486 ± 0.0006 ms	0.0488 ± 0.00056 ms	0.997 ± 0.017
hyperbolic_serre_green_naghdi_1d/hyperbolic_serre_green_naghdi_dingemans.jl - rhs!:	4.22 ± 0.03 μs	4.25 ± 0.031 μs	0.993 ± 0.01
kdv_1d/kdv_1d_basic.jl - rhs!:	1.47 ± 0.02 μs	1.47 ± 0.02 μs	1 ± 0.019
kdv_1d/kdv_1d_implicit.jl - rhs!:	1.45 ± 0.02 μs	1.41 ± 0.019 μs	1.03 ± 0.02
serre_green_naghdi_1d/serre_green_naghdi_well_balanced.jl - rhs!:	0.201 ± 0.0091 ms	0.204 ± 0.0089 ms	0.983 ± 0.062
svaerd_kalisch_1d/svaerd_kalisch_1d_dingemans_relaxation.jl - rhs!:	0.147 ± 0.0047 ms	0.149 ± 0.0052 ms	0.984 ± 0.047
time_to_load	1.94 ± 0.022 s	1.93 ± 0.0067 s	1.01 ± 0.012

Memory benchmarks

	main	10e8528...	main / 10e8528...
bbm_1d/bbm_1d_basic.jl - rhs!:	1 allocs: 4.12 kB	1 allocs: 4.12 kB	1
bbm_1d/bbm_1d_fourier.jl - rhs!:	1 allocs: 4.12 kB	1 allocs: 4.12 kB	1
bbm_bbm_1d/bbm_bbm_1d_basic_reflecting.jl - rhs!:	5 allocs: 1.17 kB	5 allocs: 1.17 kB	1
bbm_bbm_1d/bbm_bbm_1d_dg.jl - rhs!:	10 allocs: 8.62 kB	10 allocs: 8.62 kB	1
bbm_bbm_1d/bbm_bbm_1d_relaxation.jl - rhs!:	2 allocs: 8.25 kB	2 allocs: 8.25 kB	1
bbm_bbm_1d/bbm_bbm_1d_upwind_relaxation.jl - rhs!:	2 allocs: 8.25 kB	2 allocs: 8.25 kB	1
hyperbolic_serre_green_naghdi_1d/hyperbolic_serre_green_naghdi_dingemans.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
kdv_1d/kdv_1d_basic.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
kdv_1d/kdv_1d_implicit.jl - rhs!:	0 allocs: 0 B	0 allocs: 0 B
serre_green_naghdi_1d/serre_green_naghdi_well_balanced.jl - rhs!:	0.075 k allocs: 0.66 MB	0.075 k allocs: 0.66 MB	1
svaerd_kalisch_1d/svaerd_kalisch_1d_dingemans_relaxation.jl - rhs!:	0.042 k allocs: 0.315 MB	0.042 k allocs: 0.315 MB	1
time_to_load	0.153 k allocs: 14.5 kB	0.153 k allocs: 14.5 kB	1

[JoshuaLampert]

Nice, thanks! I think having the non-transparent logo as favicon is fine. Otherwise it might be difficult to see.