Docs: cite the python-multiplatform notebook E2E as the evidence for S5.2 to S5.5 #95

python-multiplatform #26 landed (#170, develop 844cf291). Its notebook E2E passes 20 of 20 against this package's develop wheel. SPEC S5.2, S5.3, S5.4, S5.5 and §8, and PROJECT §3, still say that evidence is pending. Cite it instead. The statuses stay partial, because SPEC counts evidence that lives only outside this repository as partial. Docs only; test counts unchanged.