[DF][NFC] Improve Cache documentation
[DF][NFC] Improve Cache documentation

Fixes ROOT-9646.

olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,karies/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,olifre/root,olifre/root,karies/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,root-mirror/root,root-mirror/root,olifre/root