[doc] Update CONTRIBUTING.md to include contribution opportunities (#3794)
[doc] Update CONTRIBUTING.md to include contribution opportunities (#3794)

Co-authored-by: Vissidarte-Herman <bb38b48046b6557306e3b6798e1a0188f4c150c8@users.noreply.github.com>
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi