[doc] Cherrypicks sparse matrix doc changes into v1.3.0 release branch#6770

Merged

PENGUINLIONG merged 1 commit intotaichi-dev:rc-v1.3.0from FantasyVR:cherry-pick-sm-doc

Nov 30, 2022

+14-13

Commits on Nov 30, 2022

[doc] Update sparse matrix document (taichi-dev#6719 )

committed