Add corpus-bench example

[fintelia]

Example output when run on the QOI benchmark suite:

Directory                                     Ratio             Encode                    Decode
---------                                    -------     --------------------      --------------------
qoi_benchmark_suite/images/pngimg             20.62%      42 mps   0.16 GiB/s       69 mps   0.26 GiB/s
qoi_benchmark_suite/images/icon_512            7.79%      76 mps   0.28 GiB/s       96 mps   0.36 GiB/s
qoi_benchmark_suite/images/textures_photo     61.56%      27 mps   0.08 GiB/s       56 mps   0.16 GiB/s
qoi_benchmark_suite/images/photo_kodak        61.44%      24 mps   0.07 GiB/s       52 mps   0.15 GiB/s
qoi_benchmark_suite/images/screenshot_game    25.03%      43 mps   0.14 GiB/s       72 mps   0.23 GiB/s
qoi_benchmark_suite/images/icon_64            27.97%      32 mps   0.12 GiB/s       56 mps   0.21 GiB/s
qoi_benchmark_suite/images/photo_tecnick      55.88%      27 mps   0.08 GiB/s       52 mps   0.15 GiB/s
qoi_benchmark_suite/images/textures_pk        63.59%      32 mps   0.09 GiB/s       55 mps   0.16 GiB/s
qoi_benchmark_suite/images/photo_wikipedia    61.83%      30 mps   0.09 GiB/s       53 mps   0.15 GiB/s
qoi_benchmark_suite/images/textures_pk01      36.79%      27 mps   0.10 GiB/s       52 mps   0.20 GiB/s
qoi_benchmark_suite/images/textures_plants    24.33%      41 mps   0.15 GiB/s       66 mps   0.25 GiB/s
qoi_benchmark_suite/images/textures_pk02      43.02%      30 mps   0.11 GiB/s       48 mps   0.18 GiB/s
qoi_benchmark_suite/images/screenshot_web      9.14%      76 mps   0.29 GiB/s       98 mps   0.37 GiB/s

Total                                        28.472%      40 mps   0.14 GiB/s       66 mps   0.22 GiB/s

[HeroicKatora]

Using an example seems reasonable here.