fix(04): fix grammar, minor clarification
fix(04): fix grammar, minor clarification

fpvandoorn/tutorial,leanprover/tutorial,Hodapp87/cs6460_project,leanprover/tutorial,avigad/tutorial,leanprover/tutorial,soonhokong/lean-tutorial,fpvandoorn/tutorial,Hodapp87/cs6460_project,avigad/tutorial,Hodapp87/cs6460_project,fpvandoorn/tutorial,avigad/tutorial,soonhokong/lean-tutorial,soonhokong/lean-tutorial