doc(doc/lua): add universe polymorphism elimator example
doc(doc/lua): add universe polymorphism elimator example

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

fpvandoorn/lean2,javra/lean,leodemoura/lean,rlewis1988/lean,c-cube/lean,leanprover-community/lean,leanprover/lean,soonhokong/lean-osx,leodemoura/lean,fpvandoorn/lean,javra/lean,soonhokong/lean-windows,rlewis1988/lean,htzh/lean,UlrikBuchholtz/lean,fgdorais/lean,rlewis1988/lean,dselsam/lean,dselsam/lean,htzh/lean,javra/lean,c-cube/lean,dselsam/lean,avigad/lean,soonhokong/lean-osx,eigengrau/lean,johoelzl/lean,UlrikBuchholtz/lean,soonhokong/lean-windows,eigengrau/lean,soonhokong/lean-windows,digama0/lean,digama0/lean,fpvandoorn/lean2,javra/lean,leanprover-community/lean,htzh/lean,fpvandoorn/lean2,leanprover-community/lean,fgdorais/lean,UlrikBuchholtz/lean,avigad/lean,digama0/lean,fgdorais/lean,soonhokong/lean,fgdorais/lean,fpvandoorn/lean,leodemoura/lean,eigengrau/lean,javra/lean,leanprover/lean,levnach/lean,eigengrau/lean,avigad/lean,soonhokong/travis_test,leodemoura/lean,johoelzl/lean,soonhokong/lean,fpvandoorn/lean,Kha/lean,fpvandoorn/lean,sp3ctum/lean,leanprover-community/lean,leanprover-community/lean,soonhokong/lean-windows,leanprover/lean,dselsam/lean,sp3ctum/lean,fgdorais/lean,avigad/lean,leodemoura/lean,digama0/lean,soonhokong/travis_test,Kha/lean,avigad/lean,c-cube/lean,soonhokong/lean-osx,avigad/lean,leodemoura/lean,rlewis1988/lean,sp3ctum/lean,rlewis1988/lean,johoelzl/lean,johoelzl/lean,levnach/lean,UlrikBuchholtz/lean,soonhokong/travis_test,fpvandoorn/lean,levnach/lean,dselsam/lean,sp3ctum/lean,UlrikBuchholtz/lean,levnach/lean,soonhokong/lean-osx,soonhokong/lean-osx,Kha/lean,fpvandoorn/lean2,levnach/lean,leanprover/lean,Kha/lean,johoelzl/lean,fgdorais/lean,fpvandoorn/lean,Kha/lean,leanprover-community/lean,Kha/lean,htzh/lean,digama0/lean,soonhokong/lean,johoelzl/lean,rlewis1988/lean,eigengrau/lean,leanprover/lean,sp3ctum/lean,htzh/lean,soonhokong/lean,c-cube/lean,digama0/lean,leanprover/lean,soonhokong/travis_test,dselsam/lean,c-cube/lean,fpvandoorn/lean2,soonhokong/lean-windows,soonhokong/lean