feat: add readme to divan_compat

[GuillaumeLagrange]

No description provided.

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #75 will not alter performance

_{Comparing add-divan-todo (eae1195) with main (38f7270)}

Summary

✅ 152 untouched benchmarks

[codspeed-hq]

CodSpeed Walltime Performance Report

Merging #75 will degrade performances by 50.48%

_{Comparing add-divan-todo (eb612f9) with main (38f7270)}

Summary

⚡ 3 improvements
❌ 5 regressions
✅ 90 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
⚡	recursive[10]	6.8 µs	6.6 µs	+3.85%
❌	graph_coloring[3]	1 µs	1.1 µs	-3.37%
❌	graph_coloring[5]	4.4 µs	4.5 µs	-3.71%
❌	graph_coloring[6]	4.3 µs	4.8 µs	-9.76%
❌	hamiltonian_cycle[4]	4.6 µs	4.7 µs	-3.05%
⚡	permutations[6]	73.6 µs	69.3 µs	+6.23%
❌	generate_gray_code[5]	1.9 µs	3.8 µs	-50.48%
⚡	system_time	6.8 µs	6.6 µs	+3.1%